utility calculator

Paint Calculator

Use our free paint calculator to estimate how much paint you need for any room. Shows coverage, cost, and number of gallons required.

Formula Verified by Dr. Arthur Pendelton, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Project Rooms

Length (ft)ft

Width (ft)ft

Height (ft)ft

Paint the Ceiling in this room

Room Layout Visualizer

Wall List & Status

North(14′×8′)Painted

East(12′×8′)Painted

South(14′×8′)Painted

West(12′×8′)Painted

Results

Total Wall Area371 sq ft

Ceiling Area0 sq ft

Net Surface Area

371 sq ft

Paint & Primer Buy List

Wall Paint (eggshell)

1.98 gal exact needed

2 Gallons

approx. $90

Estimated Project Budget

Paint & Primer Cost$90.00

Grand Total Budget

$90.00

Bookmark this paint calculator

Save this page to quickly run room dimensions, sheens, and cost estimates while standing in the home improvement store aisle.

Formula

Advanced Multi-Room Paint Formulas

Wall Area = 2 × (L + W) × H (Per Active Wall)
Exclusions = [ Doors × 21 ] + [ Windows × 12 ] + presets
Net Wall Area = Wall Area - Exclusions
Coated Area = Net Area × Texture Factor × Coats
Gallons Needed = Coated Area / Sheen Coverage Rate

Gross areas are calculated per active wall. Exclusions are deducted from standard walls first, and remaining exclusions from accent walls. Net areas are multiplied by wall texture factors (medium: 1.15x, rough: 1.30x) and coat count. Finally, they are divided by sheen coverage constants.

Step by step

How the calculation works

1Add rooms to your project using the tabs and "+ Add Room" button.
2For the selected room, input dimensions (Length, Width, Height) in feet.
3Toggle the "Include Ceiling" checkbox to include ceiling calculations.
4Click individual walls in the unfolded visual box to toggle them off or set them as Accent Walls.
5Increase door and window counts using the common size presets.
6Adjust texture factors if walls or ceilings are knockdown, orange-peel, stucco, or popcorn.
7Check the cost options panel to calculate DIY supplies and hire painter rates.
8Review the consolidated shopping list and total project budget in the results panel.

Example

Example Estimating Walkthrough

A project consists of a Bedroom (12ft × 14ft × 8ft) and a Bathroom (8ft × 10ft × 8ft). The bedroom has standard walls and eggshell paint (375 sq ft/gal). The bathroom has semi-gloss paint and the ceiling is painted. The calculator compiles standard wall areas, subtracts all doors and windows, applies texture modifiers, adds up the separate sheens, and provides a shopping guide recommending 3 gallons of wall paint, 1 gallon of ceiling paint, and 1 gallon of semi-gloss bathroom paint, totaling the costs instantly.

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Inputs

Project Rooms

Length (ft)ft

Width (ft)ft

Height (ft)ft

Paint the Ceiling in this room

Room Layout Visualizer

Wall List & Status

North(14′×8′)Painted

East(12′×8′)Painted

South(14′×8′)Painted

West(12′×8′)Painted

How to understand and use this calculator

Quick Answer: How Much Paint Do I Need?

How much paint do I need? The amount of paint you need depends on the total wall area, the number of coats, and the paint coverage rate.

The basic formulas are:

Total Wall Area = (2 × Length × Height) + (2 × Width × Height)
Paintable Area = Total Wall Area - (Door Area + Window Area)
Paint Needed = (Paintable Area × Number of Coats) ÷ Coverage Rate

If you need to calculate the raw floor area or overall room dimensions beforehand, check out our Square Footage Calculator or perform detailed division checks with our Long Division Calculator.

Worked Example:

Room size: 12 ft × 10 ft × 8 ft
Openings: 1 door (21 sq ft) and 2 windows (12 sq ft each)
Total wall area: 352 sq ft
Paintable area: 307 sq ft
Coverage: 350 sq ft per gallon
Paint needed for 2 coats: (307 × 2) ÷ 350 = 1.75 gallons (round up to 2 gallons)

What is a Paint Calculator?

A paint calculator (also called a paint estimator) is a tool that helps you determine exactly how much paint you'll need for a painting project. Instead of guessing and buying too much or too little paint, you can use this tool to get an accurate estimate.

Why use a paint calculator?

Saves money — Buy only the paint you need, reducing wasted extra gallons.
Saves time — Avoid multiple trips to the hardware store for more paint.
Accurate planning — Know exactly how much to budget for paint and labor.
Reduces waste — Excess paint can be expensive to buy and hard to dispose of safely.

When to use a paint calculator:

Painting a single room or accent wall.
Painting multiple rooms or an entire level.
Painting the exterior of a house or garage.
Commercial painting projects or construction jobs.
DIY home improvement and renovation projects.

How to Calculate How Much Paint You Need

Learning how much paint you will need is essential. Here is the step-by-step formula:

Step 1: Calculate the total wall area

Total Wall Area = (2 × Length × Height) + (2 × Width × Height)

Example: For a 12 ft × 10 ft room with 8 ft ceilings:

Total Wall Area = (2 × 12 × 8) + (2 × 10 × 8) = 192 + 160 = 352 sq ft

Step 2: Calculate the area of doors and windows

Standard door dimensions:

Standard Door: 3 ft × 7 ft = 21 sq ft
Standard Window: 3 ft × 4 ft = 12 sq ft

Example: 1 door (21 sq ft) + 2 windows (24 sq ft) = 45 sq ft of openings.

Step 3: Calculate paintable area

Paintable Area = Total Wall Area - (Door Area + Window Area)

Example: Paintable Area = 352 - 45 = 307 sq ft

Step 4: Calculate paint needed

Paint Needed = (Paintable Area × Number of Coats) ÷ Coverage Rate

Example: 1 coat: 307 ÷ 350 = 0.88 gallons; 2 coats: (307 × 2) ÷ 350 = 1.75 gallons (round up to 2 gallons).

Step 5: Calculate total cost

Total Cost = Paint Needed × Price Per Gallon

Example: 2 gallons × $35 = $70

To calculate percentage waste buffers, sales taxes, or contractor markups, use our Percentage Calculator or the Markup Calculator.

How to Use This Paint Calculator — Step by Step

Using our paint coverage calculator is simple:

Step 1: Measure your room — Measure the length, width, and height of the room in feet or meters.
Step 2: Count doors and windows — Count the number of doors and windows in the room.
Step 3: Decide on number of coats — 1 coat: Touch-ups or color matching; 2 coats: Standard for most rooms (recommended); 3 coats: Dramatic color changes or dark colors.
Step 4: Check the paint can for coverage rate — Most paints cover 350-400 sq ft per gallon. Check the label for exact coverage.
Step 5: Enter all values into the calculator — Input dimensions, openings, coats, and coverage rate.
Step 6: Review your results — Check total wall area, paintable area, paint needed (gallons or liters), and total cost.

Room Dimensions — Measuring Your Space

Accurate measurements are crucial for a correct paint estimation. Here's how to measure your room properly:

Measuring length and width:

Measure each wall from corner to corner.
For rectangular rooms, measure two adjacent walls (length and width).
For irregular rooms, break the room into smaller rectangles and add the areas.

Measuring height:

Measure from the floor to the ceiling. If the ceiling is sloped, measure the average height.

Measuring irregular rooms:

For rooms with alcoves, measure each section separately and add the areas together.
For circular rooms, measure the diameter and use the circle area formula: 3.14159 × radius × radius.

Pro tip: Always measure twice to ensure accuracy. Add a 10% safety buffer to your estimate for mistakes and waste.

Doors and Windows — Subtracting Openings

You don't need to paint over doors and windows. Here are standard sizes to help you account for them:

Standard door sizes:

Standard Interior/Exterior Door: 3 ft × 7 ft = 21 sq ft
French Door: 5 ft × 7 ft = 35 sq ft
Sliding Glass Door: 6 ft × 7 ft = 42 sq ft

Standard window sizes:

Small Window: 2 ft × 3 ft = 6 sq ft
Standard Window: 3 ft × 4 ft = 12 sq ft
Large Window: 4 ft × 5 ft = 20 sq ft
Picture Window: 5 ft × 6 ft = 30 sq ft

Custom openings: If your doors or windows are non-standard, multiply their width by height to get the exact area, and enter it in the custom exclusions field.

Pro tip: You don't need to subtract the door or window frame — just the opening itself. The frame is painted separately with trim paint.

Number of Coats — How Many Layers Do You Need?

The number of paint coats you apply affects how much paint you need. Here is a guide:

Same color, good condition (1-2 coats): Light refresh of the room.
Different color (2 coats): Standard requirement for rich coverage.
Dramatic color change (3 coats): Dark to light transitions need extra coverage.
New drywall (2 coats + primer): Highly porous surfaces need preparation and sealing.
Dark walls going light (3 coats): Prevents the old dark color from bleeding through.
Textured walls (3 coats): Texture absorbs significantly more paint.
Primer coat (1 coat): Recommended for all new or stained surfaces.

General rule: Two coats are recommended for most rooms. One coat is rarely enough for a professional-looking finish.

Paint Coverage Rates — What to Expect

The coverage rate is the most important factor in determining how much paint you need:

Flat/Matte: 350-400 sq ft/gal (8.6-9.8 m²/L) - Hides imperfections best.
Eggshell: 350-400 sq ft/gal (8.6-9.8 m²/L) - Low sheen, highly durable.
Satin: 300-350 sq ft/gal (7.4-8.6 m²/L) - Washable, very popular.
Semi-Gloss: 300-350 sq ft/gal (7.4-8.6 m²/L) - High durability, moisture-resistant.
Gloss: 250-300 sq ft/gal (6.1-7.4 m²/L) - Extreme durability, high sheen.
Primer: 300-400 sq ft/gal (7.4-9.8 m²/L) - Prepares and seals surfaces.
Exterior Paint: 250-350 sq ft/gal (6.1-8.6 m²/L) - Weather-resistant.

Surface type adjustments:

Smooth drywall: Standard coverage.
Textured drywall: 10-20% more paint.
Plaster: 10-15% more paint.
Brick/Concrete: 20-30% more paint (very porous).
Wood (unpainted): 15-20% more paint.
Ceiling: Standard coverage.

Types of Paint — Which One Should You Choose?

Choosing the right finish ensures paint durability and aesthetics:

Flat/Matte: Best for ceilings and low-traffic rooms. Pros: Hides imperfections, no glare. Cons: Hard to wash, stains show.
Eggshell: Best for living rooms and dining rooms. Pros: Slight sheen, washable. Cons: Medium durability.
Satin: Best for hallways, kids' rooms, and kitchens. Pros: Durable, washable. Cons: Shows wall imperfections.
Semi-Gloss: Best for bathrooms, kitchens, and trim. Pros: Moisture-resistant, very durable. Cons: Shiny, highlights flaws.
Gloss: Best for doors, trim, and cabinets. Pros: Extremely durable, easy to clean. Cons: Highly reflective, shows every flaw.
Primer: Best for new surfaces and color changes. Pros: Prepares surface, covers stains. Cons: Not a finished topcoat.

Exterior Paint Calculator — Special Considerations

When estimating exterior painting projects, keep these differences in mind:

Surface Porosity — Wood, brick, stucco, and concrete absorb significantly more paint than smooth interior drywall. Plan on an additional 15-20% volume buffer.
Weather Conditions — Temperature and humidity affect drying and coverage rates.
Preparation — Scraping, sanding, pressure washing, and spot-priming are critical for exterior adhesion.
Coats — Standard exterior projects require a minimum of 2 coats plus 1 base primer coat for bare sections.

For other heavy construction materials like concrete foundations or paving, consult our blog article on Concrete Volume Estimation.

Interior Painting Cost Calculator — Budget Estimator

Use our interior painting cost calculator to estimate your budget:

Cost components:

Paint cost — Price per gallon × number of gallons.
Supplies — Brushes, rollers, trays, tape, drop cloths.
Labor — Professional labor fees (if hiring).
Prep materials — Sandpaper, spackle, primer.

Average paint cost per gallon:

Budget Paint: $15 - $25
Mid-Range Paint: $25 - $45
Premium Paint: $45 - $70+
Primer: $15 - $30

Surface Preparation Tips

Proper surface preparation ensures better paint adhesion and a longer-lasting finish:

Clean — Wash walls with soapy water to remove dirt, dust, and grease.
Repair — Fill holes, dents, and cracks with spackle; let dry.
Sand — Sand rough spots and spackled areas smooth.
Prime — Apply primer to new drywall, bare wood, or stained surfaces.
Tape — Apply painter's tape along trim, baseboards, and ceiling edges.
Protect — Cover floors and furniture with canvas or plastic drop cloths.

Practice Problems

Problem 1: A room measures 14 ft × 12 ft × 9 ft. It has 2 doors and 3 windows. How much wall area needs to be painted?

*Solution:* Total Wall Area = (2 × 14 × 9) + (2 × 12 × 9) = 252 + 216 = 468 sq ft. Doors: 2 × 21 = 42 sq ft. Windows: 3 × 12 = 36 sq ft. Exclusions = 78 sq ft. Net Paintable Area = 468 - 78 = 390 sq ft.

Problem 2: From Problem 1, if paint covers 350 sq ft per gallon, and you want 2 coats, how many gallons do you need?

*Solution:* Total paintable area with 2 coats = 390 × 2 = 780 sq ft. Gallons needed = 780 ÷ 350 = 2.23 gallons. Round up to 3 gallons.

Problem 3: You're painting a room with 400 sq ft of paintable wall area. Paint costs $40 per gallon and covers 400 sq ft per gallon. How much will 2 coats cost?

*Solution:* Gallons needed for 2 coats = (400 × 2) ÷ 400 = 2 gallons. Total cost = 2 × $40 = $80.

Problem 4: You're painting a room that is 10 ft × 8 ft × 8 ft. There are no doors and 2 windows. How much paint is needed for 2 coats (coverage = 350 sq ft/gal)?

*Solution:* Total Wall Area = (2 × 10 × 8) + (2 × 8 × 8) = 160 + 128 = 288 sq ft. Windows: 2 × 12 = 24 sq ft. Net Area = 288 - 24 = 264 sq ft. For 2 coats: 264 × 2 = 528 sq ft. Gallons = 528 ÷ 350 = 1.51 gallons. Round up to 2 gallons.

Problem 5: A room has 380 sq ft of paintable wall area. You want to use premium paint that costs $55 per gallon and covers 350 sq ft per gallon. What is the total paint cost for 2 coats?

*Solution:* Gallons for 2 coats = (380 × 2) ÷ 350 = 2.18 gallons. Round up to 3 gallons. Total cost = 3 × $55 = $165.

Common Paint Calculation Mistakes

Avoid these frequent errors to ensure your project goes smoothly:

Forgetting to measure all walls — Measuring only length and width, ignoring height.
Not subtracting doors and windows — Buying excess paint by calculating solid walls.
Ignoring the number of coats — Forgetting to multiply your square footage by 2 for the second coat.
Misreading coverage rates — Using the maximum coverage rate for rough or porous surfaces.
Not accounting for trim and ceilings — Forgetting to add separate volume estimates for these trims.
Rounding down instead of up — Buying exactly 2.1 gallons, leaving you short near the end of the project.
Forgetting the waste factor — Buying no extra paint for spills, brush/roller loading, or future touch-ups. Always add a 10% buffer.
Ignoring surface porosity — Painting raw wood or brick without adding 20% to your volume estimate.

What This Calculator Can and Cannot Do

This calculator can help with:

Estimating paint volumes for multiple rooms in a single project.
Deducting standard doors, sliding doors, and windows using presets.
Modeling accent walls and skipped walls interactively.
Computing primer needs separately from topcoat paint.
Formulating a complete budget including DIY supplies and professional labor.

This calculator cannot do:

Predict exact paint absorption on highly unusual surfaces (consult manufacturer).
Detail trim linear footage requirements automatically.
Account for paint spills or extreme spraying waste (add a 10% buffer).

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Calculate flooring epoxy requirements for garages and concrete decks.

Frequently Asked Questions

What is a paint calculator?+

A paint calculator is a tool that helps you estimate how much paint you'll need for a room or building by analyzing room dimensions, doors, windows, coats, and texture absorption rates.

How much paint do I need for a 12×12 room?+

For a standard 12 ft × 12 ft × 8 ft room (approx. 384 sq ft of walls), you'll need about 1 gallon for 1 coat or 2 gallons for 2 coats (rounded up from 1.75).

How much does a gallon of paint cover?+

A standard gallon covers about 350 to 400 square feet of smooth drywall. Textured, rough, or porous surfaces reduce coverage to 250-300 sq ft per gallon.

How many coats of paint do I need?+

Most interior projects require 2 coats. A refresh of the exact same color may need 1 coat, while dramatic dark-to-light changes may require 3 coats.

How much paint do I need for exterior painting?+

Exterior painting typically needs 2 coats. Exterior surfaces are more porous (wood, brick, stucco), so add a 15-20% coverage buffer to prevent running short.

Do I need primer before painting?+

Primer is highly recommended for bare drywall, new wood, stained areas, or when making a drastic color change (e.g. dark navy to white). It seals the surface so your topcoat adheres uniformly.

How do I measure an irregular room?+

Break the room layout down into smaller rectangular sections, calculate the wall areas for each section, and sum them. Or add them as separate rooms in our calculator!

How much does it cost to paint a room?+

DIY painting materials and supplies cost between $50 and $200 per room. Hiring a professional painter averages $300 to $800 per room depending on labor rates.

Advanced Multi-Room Paint Formulas

Wall Area = 2 × (L + W) × H (Per Active Wall) Exclusions = [ Doors × 21 ] + [ Windows × 12 ] + presets Net Wall Area = Wall Area - Exclusions Coated Area = Net Area × Texture Factor × Coats Gallons Needed = Coated Area / Sheen Coverage Rate

How the calculation works

1Add rooms to your project using the tabs and "+ Add Room" button.

2For the selected room, input dimensions (Length, Width, Height) in feet.

3Toggle the "Include Ceiling" checkbox to include ceiling calculations.

4Click individual walls in the unfolded visual box to toggle them off or set them as Accent Walls.

5Increase door and window counts using the common size presets.

6Adjust texture factors if walls or ceilings are knockdown, orange-peel, stucco, or popcorn.

7Check the cost options panel to calculate DIY supplies and hire painter rates.

8Review the consolidated shopping list and total project budget in the results panel.

Example Estimating Walkthrough

How to understand and use this calculator

Quick Answer: How Much Paint Do I Need?

How much paint do I need? The amount of paint you need depends on the total wall area, the number of coats, and the paint coverage rate.

The basic formulas are:

Total Wall Area = (2 × Length × Height) + (2 × Width × Height)
Paintable Area = Total Wall Area - (Door Area + Window Area)
Paint Needed = (Paintable Area × Number of Coats) ÷ Coverage Rate

If you need to calculate the raw floor area or overall room dimensions beforehand, check out our Square Footage Calculator or perform detailed division checks with our Long Division Calculator.

Worked Example:

Room size: 12 ft × 10 ft × 8 ft
Openings: 1 door (21 sq ft) and 2 windows (12 sq ft each)
Total wall area: 352 sq ft
Paintable area: 307 sq ft
Coverage: 350 sq ft per gallon
Paint needed for 2 coats: (307 × 2) ÷ 350 = 1.75 gallons (round up to 2 gallons)

What is a Paint Calculator?

Why use a paint calculator?

Saves money — Buy only the paint you need, reducing wasted extra gallons.
Saves time — Avoid multiple trips to the hardware store for more paint.
Accurate planning — Know exactly how much to budget for paint and labor.
Reduces waste — Excess paint can be expensive to buy and hard to dispose of safely.

When to use a paint calculator:

Painting a single room or accent wall.
Painting multiple rooms or an entire level.
Painting the exterior of a house or garage.
Commercial painting projects or construction jobs.
DIY home improvement and renovation projects.

How to Calculate How Much Paint You Need

Learning how much paint you will need is essential. Here is the step-by-step formula:

Step 1: Calculate the total wall area

Total Wall Area = (2 × Length × Height) + (2 × Width × Height)

Example: For a 12 ft × 10 ft room with 8 ft ceilings:

Total Wall Area = (2 × 12 × 8) + (2 × 10 × 8) = 192 + 160 = 352 sq ft

Step 2: Calculate the area of doors and windows

Standard door dimensions:

Standard Door: 3 ft × 7 ft = 21 sq ft
Standard Window: 3 ft × 4 ft = 12 sq ft

Example: 1 door (21 sq ft) + 2 windows (24 sq ft) = 45 sq ft of openings.

Step 3: Calculate paintable area

Paintable Area = Total Wall Area - (Door Area + Window Area)

Example: Paintable Area = 352 - 45 = 307 sq ft

Step 4: Calculate paint needed

Paint Needed = (Paintable Area × Number of Coats) ÷ Coverage Rate

Example: 1 coat: 307 ÷ 350 = 0.88 gallons; 2 coats: (307 × 2) ÷ 350 = 1.75 gallons (round up to 2 gallons).

Step 5: Calculate total cost

Total Cost = Paint Needed × Price Per Gallon

Example: 2 gallons × $35 = $70

To calculate percentage waste buffers, sales taxes, or contractor markups, use our Percentage Calculator or the Markup Calculator.

How to Use This Paint Calculator — Step by Step

Using our paint coverage calculator is simple:

Step 1: Measure your room — Measure the length, width, and height of the room in feet or meters.
Step 2: Count doors and windows — Count the number of doors and windows in the room.
Step 3: Decide on number of coats — 1 coat: Touch-ups or color matching; 2 coats: Standard for most rooms (recommended); 3 coats: Dramatic color changes or dark colors.
Step 4: Check the paint can for coverage rate — Most paints cover 350-400 sq ft per gallon. Check the label for exact coverage.
Step 5: Enter all values into the calculator — Input dimensions, openings, coats, and coverage rate.
Step 6: Review your results — Check total wall area, paintable area, paint needed (gallons or liters), and total cost.

Room Dimensions — Measuring Your Space

Accurate measurements are crucial for a correct paint estimation. Here's how to measure your room properly:

Measuring length and width:

Measure each wall from corner to corner.
For rectangular rooms, measure two adjacent walls (length and width).
For irregular rooms, break the room into smaller rectangles and add the areas.

Measuring height:

Measure from the floor to the ceiling. If the ceiling is sloped, measure the average height.

Measuring irregular rooms:

For rooms with alcoves, measure each section separately and add the areas together.
For circular rooms, measure the diameter and use the circle area formula: 3.14159 × radius × radius.

Pro tip: Always measure twice to ensure accuracy. Add a 10% safety buffer to your estimate for mistakes and waste.

Doors and Windows — Subtracting Openings

You don't need to paint over doors and windows. Here are standard sizes to help you account for them:

Standard door sizes:

Standard Interior/Exterior Door: 3 ft × 7 ft = 21 sq ft
French Door: 5 ft × 7 ft = 35 sq ft
Sliding Glass Door: 6 ft × 7 ft = 42 sq ft

Standard window sizes:

Small Window: 2 ft × 3 ft = 6 sq ft
Standard Window: 3 ft × 4 ft = 12 sq ft
Large Window: 4 ft × 5 ft = 20 sq ft
Picture Window: 5 ft × 6 ft = 30 sq ft

Custom openings: If your doors or windows are non-standard, multiply their width by height to get the exact area, and enter it in the custom exclusions field.

Pro tip: You don't need to subtract the door or window frame — just the opening itself. The frame is painted separately with trim paint.

Number of Coats — How Many Layers Do You Need?

The number of paint coats you apply affects how much paint you need. Here is a guide:

Same color, good condition (1-2 coats): Light refresh of the room.
Different color (2 coats): Standard requirement for rich coverage.
Dramatic color change (3 coats): Dark to light transitions need extra coverage.
New drywall (2 coats + primer): Highly porous surfaces need preparation and sealing.
Dark walls going light (3 coats): Prevents the old dark color from bleeding through.
Textured walls (3 coats): Texture absorbs significantly more paint.
Primer coat (1 coat): Recommended for all new or stained surfaces.

General rule: Two coats are recommended for most rooms. One coat is rarely enough for a professional-looking finish.

Paint Coverage Rates — What to Expect

The coverage rate is the most important factor in determining how much paint you need:

Flat/Matte: 350-400 sq ft/gal (8.6-9.8 m²/L) - Hides imperfections best.
Eggshell: 350-400 sq ft/gal (8.6-9.8 m²/L) - Low sheen, highly durable.
Satin: 300-350 sq ft/gal (7.4-8.6 m²/L) - Washable, very popular.
Semi-Gloss: 300-350 sq ft/gal (7.4-8.6 m²/L) - High durability, moisture-resistant.
Gloss: 250-300 sq ft/gal (6.1-7.4 m²/L) - Extreme durability, high sheen.
Primer: 300-400 sq ft/gal (7.4-9.8 m²/L) - Prepares and seals surfaces.
Exterior Paint: 250-350 sq ft/gal (6.1-8.6 m²/L) - Weather-resistant.

Surface type adjustments:

Smooth drywall: Standard coverage.
Textured drywall: 10-20% more paint.
Plaster: 10-15% more paint.
Brick/Concrete: 20-30% more paint (very porous).
Wood (unpainted): 15-20% more paint.
Ceiling: Standard coverage.

Types of Paint — Which One Should You Choose?

Choosing the right finish ensures paint durability and aesthetics:

Flat/Matte: Best for ceilings and low-traffic rooms. Pros: Hides imperfections, no glare. Cons: Hard to wash, stains show.
Eggshell: Best for living rooms and dining rooms. Pros: Slight sheen, washable. Cons: Medium durability.
Satin: Best for hallways, kids' rooms, and kitchens. Pros: Durable, washable. Cons: Shows wall imperfections.
Semi-Gloss: Best for bathrooms, kitchens, and trim. Pros: Moisture-resistant, very durable. Cons: Shiny, highlights flaws.
Gloss: Best for doors, trim, and cabinets. Pros: Extremely durable, easy to clean. Cons: Highly reflective, shows every flaw.
Primer: Best for new surfaces and color changes. Pros: Prepares surface, covers stains. Cons: Not a finished topcoat.

Exterior Paint Calculator — Special Considerations

When estimating exterior painting projects, keep these differences in mind:

Surface Porosity — Wood, brick, stucco, and concrete absorb significantly more paint than smooth interior drywall. Plan on an additional 15-20% volume buffer.
Weather Conditions — Temperature and humidity affect drying and coverage rates.
Preparation — Scraping, sanding, pressure washing, and spot-priming are critical for exterior adhesion.
Coats — Standard exterior projects require a minimum of 2 coats plus 1 base primer coat for bare sections.

For other heavy construction materials like concrete foundations or paving, consult our blog article on Concrete Volume Estimation.

Interior Painting Cost Calculator — Budget Estimator

Use our interior painting cost calculator to estimate your budget:

Cost components:

Paint cost — Price per gallon × number of gallons.
Supplies — Brushes, rollers, trays, tape, drop cloths.
Labor — Professional labor fees (if hiring).
Prep materials — Sandpaper, spackle, primer.

Average paint cost per gallon:

Budget Paint: $15 - $25
Mid-Range Paint: $25 - $45
Premium Paint: $45 - $70+
Primer: $15 - $30

Surface Preparation Tips

Proper surface preparation ensures better paint adhesion and a longer-lasting finish:

Clean — Wash walls with soapy water to remove dirt, dust, and grease.
Repair — Fill holes, dents, and cracks with spackle; let dry.
Sand — Sand rough spots and spackled areas smooth.
Prime — Apply primer to new drywall, bare wood, or stained surfaces.
Tape — Apply painter's tape along trim, baseboards, and ceiling edges.
Protect — Cover floors and furniture with canvas or plastic drop cloths.

Practice Problems

Problem 1: A room measures 14 ft × 12 ft × 9 ft. It has 2 doors and 3 windows. How much wall area needs to be painted?

*Solution:* Total Wall Area = (2 × 14 × 9) + (2 × 12 × 9) = 252 + 216 = 468 sq ft. Doors: 2 × 21 = 42 sq ft. Windows: 3 × 12 = 36 sq ft. Exclusions = 78 sq ft. Net Paintable Area = 468 - 78 = 390 sq ft.

Problem 2: From Problem 1, if paint covers 350 sq ft per gallon, and you want 2 coats, how many gallons do you need?

*Solution:* Total paintable area with 2 coats = 390 × 2 = 780 sq ft. Gallons needed = 780 ÷ 350 = 2.23 gallons. Round up to 3 gallons.

Problem 3: You're painting a room with 400 sq ft of paintable wall area. Paint costs $40 per gallon and covers 400 sq ft per gallon. How much will 2 coats cost?

*Solution:* Gallons needed for 2 coats = (400 × 2) ÷ 400 = 2 gallons. Total cost = 2 × $40 = $80.

Problem 4: You're painting a room that is 10 ft × 8 ft × 8 ft. There are no doors and 2 windows. How much paint is needed for 2 coats (coverage = 350 sq ft/gal)?

*Solution:* Total Wall Area = (2 × 10 × 8) + (2 × 8 × 8) = 160 + 128 = 288 sq ft. Windows: 2 × 12 = 24 sq ft. Net Area = 288 - 24 = 264 sq ft. For 2 coats: 264 × 2 = 528 sq ft. Gallons = 528 ÷ 350 = 1.51 gallons. Round up to 2 gallons.

Problem 5: A room has 380 sq ft of paintable wall area. You want to use premium paint that costs $55 per gallon and covers 350 sq ft per gallon. What is the total paint cost for 2 coats?

*Solution:* Gallons for 2 coats = (380 × 2) ÷ 350 = 2.18 gallons. Round up to 3 gallons. Total cost = 3 × $55 = $165.

Common Paint Calculation Mistakes

Avoid these frequent errors to ensure your project goes smoothly:

Forgetting to measure all walls — Measuring only length and width, ignoring height.
Not subtracting doors and windows — Buying excess paint by calculating solid walls.
Ignoring the number of coats — Forgetting to multiply your square footage by 2 for the second coat.
Misreading coverage rates — Using the maximum coverage rate for rough or porous surfaces.
Not accounting for trim and ceilings — Forgetting to add separate volume estimates for these trims.
Rounding down instead of up — Buying exactly 2.1 gallons, leaving you short near the end of the project.
Forgetting the waste factor — Buying no extra paint for spills, brush/roller loading, or future touch-ups. Always add a 10% buffer.
Ignoring surface porosity — Painting raw wood or brick without adding 20% to your volume estimate.

What This Calculator Can and Cannot Do

This calculator can help with:

Estimating paint volumes for multiple rooms in a single project.
Deducting standard doors, sliding doors, and windows using presets.
Modeling accent walls and skipped walls interactively.
Computing primer needs separately from topcoat paint.
Formulating a complete budget including DIY supplies and professional labor.

This calculator cannot do:

Predict exact paint absorption on highly unusual surfaces (consult manufacturer).
Detail trim linear footage requirements automatically.
Account for paint spills or extreme spraying waste (add a 10% buffer).

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Frequently Asked Questions

What is a paint calculator?+

A paint calculator is a tool that helps you estimate how much paint you'll need for a room or building by analyzing room dimensions, doors, windows, coats, and texture absorption rates.

How much paint do I need for a 12×12 room?+

For a standard 12 ft × 12 ft × 8 ft room (approx. 384 sq ft of walls), you'll need about 1 gallon for 1 coat or 2 gallons for 2 coats (rounded up from 1.75).

How much does a gallon of paint cover?+

A standard gallon covers about 350 to 400 square feet of smooth drywall. Textured, rough, or porous surfaces reduce coverage to 250-300 sq ft per gallon.

How many coats of paint do I need?+

Most interior projects require 2 coats. A refresh of the exact same color may need 1 coat, while dramatic dark-to-light changes may require 3 coats.

How much paint do I need for exterior painting?+

Exterior painting typically needs 2 coats. Exterior surfaces are more porous (wood, brick, stucco), so add a 15-20% coverage buffer to prevent running short.

Do I need primer before painting?+

Primer is highly recommended for bare drywall, new wood, stained areas, or when making a drastic color change (e.g. dark navy to white). It seals the surface so your topcoat adheres uniformly.

How do I measure an irregular room?+

Break the room layout down into smaller rectangular sections, calculate the wall areas for each section, and sum them. Or add them as separate rooms in our calculator!

How much does it cost to paint a room?+

DIY painting materials and supplies cost between $50 and $200 per room. Hiring a professional painter averages $300 to $800 per room depending on labor rates.

Paint Calculator

Inputs

Project Rooms

Room Layout Visualizer

Wall List & Status

Results

Paint & Primer Buy List

Bookmark this paint calculator

Advanced Multi-Room Paint Formulas

How the calculation works

Example Estimating Walkthrough

Learn more about this calculation

Concrete Volume Guide: Slab Yardage, Waste Allowance, and Bag Estimates

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Paint Calculator

Inputs

Project Rooms

Room Layout Visualizer

Wall List & Status

Results

Paint & Primer Buy List

Bookmark this paint calculator

Key output metrics

Painted Surface Distribution

Paint Volume by Component (Gallons)

How to understand and use this calculator

Quick Answer: How Much Paint Do I Need?

What is a Paint Calculator?

How to Calculate How Much Paint You Need

How to Use This Paint Calculator — Step by Step

Room Dimensions — Measuring Your Space

Doors and Windows — Subtracting Openings

Number of Coats — How Many Layers Do You Need?

Paint Coverage Rates — What to Expect

Types of Paint — Which One Should You Choose?

Exterior Paint Calculator — Special Considerations

Interior Painting Cost Calculator — Budget Estimator

Surface Preparation Tips

Practice Problems

Common Paint Calculation Mistakes

What This Calculator Can and Cannot Do

Related concepts

Frequently Asked Questions

Advanced Multi-Room Paint Formulas

How the calculation works

Example Estimating Walkthrough

Learn more about this calculation

Concrete Volume Guide: Slab Yardage, Waste Allowance, and Bag Estimates

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Key output metrics

Painted Surface Distribution

Paint Volume by Component (Gallons)

How to understand and use this calculator

Quick Answer: How Much Paint Do I Need?

What is a Paint Calculator?

How to Calculate How Much Paint You Need

How to Use This Paint Calculator — Step by Step

Room Dimensions — Measuring Your Space

Doors and Windows — Subtracting Openings

Number of Coats — How Many Layers Do You Need?

Paint Coverage Rates — What to Expect

Types of Paint — Which One Should You Choose?

Exterior Paint Calculator — Special Considerations

Interior Painting Cost Calculator — Budget Estimator

Surface Preparation Tips

Practice Problems

Common Paint Calculation Mistakes

What This Calculator Can and Cannot Do

Related concepts

Frequently Asked Questions