Image Size Explained: Pixels, DPI, Aspect Ratio and the Exact Sizes for Print, Social Media and ID Photos

Image size: the short answer

The size of a digital image is its pixel count: how many pixels wide by how many pixels high, such as 4032 × 3024. That is the only thing that decides how much detail it holds. DPI (dots per inch) is not part of the picture at all; it is a note saying how many of those pixels to fit into each inch of paper, so it changes the printed size and nothing else. To print sharply, multiply the print size in inches by 300: a 6 × 4 inch print needs 1800 × 1200 pixels, an A4 page 2480 × 3508. On a screen, only the pixels matter.

Below are the exact pixels for common prints, for the main social networks as their own help pages state them, and for passport and visa photos, followed by a worked example that takes one phone photo to all three.

Pixels, resolution and megapixels

A photo on your phone is a grid of tiny coloured squares called pixels. Each pixel holds one colour and nothing finer; there is no detail hidden inside it waiting to be revealed. A photo described as 4032 × 3024 has 4032 pixels across each row and 3024 rows. Multiply the two and you get the total, 12,192,768 pixels, which is why it is sold as a 12-megapixel camera: one megapixel is one million pixels.

The word resolution is used for two different things. Sometimes it means the pixel dimensions (“the resolution is 1920 × 1080”), a fact about the file. Sometimes it means pixel density, how closely the pixels are packed when printed (“print it at 300 DPI”), a fact about the moment the file meets paper. When a form or a printer asks for a resolution, check which it means.

Because megapixels multiply width by height, they can mislead. A 24-megapixel camera gives photos only about 1.4 times as wide and 1.4 times as tall as a 12-megapixel phone, not twice. To judge whether a photo is big enough for something, compare pixel dimensions, width against width.

To see a photo’s pixel dimensions on a Mac, select it in Finder and choose File, Get Info; Apple says the information shown can include “image dimensions” (https://support.apple.com/guide/mac-help/get-file-folder-and-disk-information-on-mac-mchlp1774/mac). On Windows, right-click the file, choose Properties and open the Details tab. In Google Photos, open the photo and swipe up to see its details (https://support.google.com/photos/answer/6220791). The KB compression guide shows where each system shows the file size as well.

DPI vs PPI, and why the DPI tag changes only the printed size

Strictly, PPI (pixels per inch) describes images and screens, and DPI (dots per inch) describes printers, which build each pixel out of many tiny dots of ink. An inkjet rated at 4800 DPI is not printing 4800 of your pixels per inch; it lays down fine droplets to reproduce far fewer. In photo programs and upload forms, though, the two words mean the same thing, how many image pixels go into each inch of paper, and this guide says DPI.

A file does not need a DPI figure, but many carry one as a small tag. In a JPG, the tag lives in the JFIF header at the start of the file: a unit code (none, per inch or per centimetre) followed by a horizontal and a vertical density; a JPG from a camera may also carry the same numbers in its EXIF block. In a PNG, it lives in a chunk called pHYs, which stores pixels per metre rather than per inch, so 300 DPI is written as 11,811 pixels per metre. Changing either tag rewrites a few bytes and leaves every pixel exactly as it was. The only thing that changes is the size a print dialog or layout program suggests when you place the image on a page.

This is why “change my photo to 300 DPI” has two possible meanings. If you only change the tag, a 1200 × 900 photo that was tagged 72 DPI (16.7 × 12.5 inches) becomes a 1200 × 900 photo tagged 300 DPI (4 × 3 inches): the same picture with a smaller suggested print size. If you want a bigger print at 300 DPI, you need more pixels, and a tag cannot supply them. The DPI tag option in the Image Resizer writes these header fields directly, without touching the pixels, for exactly this reason.

How many pixels you need for each print size

The table gives pixels at 300 DPI, the usual target for photos held in the hand; 240 DPI, a common middle setting; and 150 DPI, which the photo lab quoted below calls the practical minimum. A-series sizes come from ISO 216, the paper size standard, which gives A4 as 210 × 297 mm, A3 as 297 × 420 mm and A2 as 420 × 594 mm (https://www.iso.org/standard/36631.html); we converted each at 25.4 mm to the inch and rounded to the nearest pixel. The last column is the megapixels needed at 300 DPI.

Read the other way round, the table shows what your own photos can do. A 12-megapixel phone photo of 4032 × 3024 pixels covers every size up to A4 at 300 DPI, and A3 at 240 DPI with little to spare (4032 against 3969, and 3024 against 2806). A2 at 300 DPI needs about 35 megapixels.

The table assumes the photo already has the paper’s shape; most need a small crop first, covered under aspect ratios below. If your photo is smaller than the 150 DPI column for the size you want, it is too small to print well at that size: choose a smaller print, or accept a softer result. Enlarging the file in software will not help, for reasons explained under upscaling.

Viewing distance: why 300 DPI is not always needed

The 300 DPI figure is a convention for prints held in the hand or seen at arm’s length, where the eye can pick out fine detail. It is not a rule of physics. Pro Lab, an Indian photo printing company, puts the usual advice in a sentence on its own file requirements page: “a minimum of 300 DPI at print size, with 150 DPI as the practical minimum” (https://support.prolab.in/design--editing-help/7NLx2KPdNGGEV6vqCjvyM4/file-resolution--quality-requirements-dpi-pixels--print-quality/7NLx2KPdNLtcCGPBH2Mcpz). That is one vendor’s guidance; the figure your own lab asks for is the one that matters, so check its page before you order.

The further away you stand, the less detail your eye can resolve, so the fewer pixels per inch a print needs to look sharp. A poster or canvas is seen from metres away; an album print or photo book page from a few centimetres, which is where 300 DPI earns its keep. Text and logos show softness before photos do. The honest test is to print a small crop at the intended size and look at it from where it will be seen.

Screens are the same idea in reverse: a phone packs its pixels very tightly because it is held close, while a television can be far coarser. The screen resolution PPI calculator works out the pixel density of any screen from its size and resolution, which shows why a photo that looks crisp on a phone can look soft on a large monitor.

Aspect ratios and cropping

Aspect ratio is the shape of an image: its width divided by its height, written as a pair of small whole numbers. 4032 × 3024 simplifies to 4:3, the shape most phone cameras use. 6000 × 4000, a common camera size, is 3:2. A square is 1:1, a widescreen video frame is 16:9, and A-series paper is 1:√2, about 1:1.414, a shape ISO 216 chose so that halving a sheet gives the next size down with the same proportions.

You cannot change an image’s shape without cropping it or distorting it, and squeezing a 4:3 photo into a square makes faces look thin, so sensible tools crop: they cut a strip off the long side until the shape matches. The aspect ratio calculator finds the missing side for any ratio; the table below does it for a 12-megapixel phone photo held sideways.

Print shapes are close to a phone’s 4:3, so prints lose only a thin strip. Portrait social shapes cut from a sideways photo can lose half of it; turning the phone upright when you take the picture saves most of that, since a 3024 × 4032 photo cropped to 4:5 keeps 3024 × 3780, 93.8% of the frame. Where the crop falls matters too; in the Image Resizer, the Crop & focus tab lets you click or drag on the photo to choose the part that must stay.

The platforms treat shape differently. Instagram keeps photos between 1.91:1 and 3:4 at their original resolution (up to 1080 pixels wide), so a 4:3 phone photo, landscape or upright, needs no crop at all. Facebook shows a Page’s profile picture as a circle; X says up to 60 pixels at the top and bottom of a header may be cropped on some screens; YouTube gives a safe area for text and logos of 1235 × 338 pixels on a minimum-size banner; and Pinterest’s ad specifications warn that Pins taller than 2:3 may be cut off in feeds.

Image sizes for social media, from each platform’s own help pages

The table contains only what we could read on each platform’s own help or specification page, with the date we read it. Where a platform gives a minimum rather than a recommendation, the table says so; where we could not open its page, the row says that rather than guess.

Sources: Instagram, Image resolution of photos you share on Instagram (https://help.instagram.com/1631821640426723); Facebook, Page profile picture and cover photo dimensions (https://www.facebook.com/help/125379114252045); X, Help with uploading a profile photo (https://help.x.com/en/managing-your-account/common-issues-when-uploading-profile-photo); LinkedIn profile photo (https://www.linkedin.com/help/linkedin/answer/a549049), background photo (https://www.linkedin.com/help/linkedin/answer/a568217) and Pages image specifications (https://www.linkedin.com/help/linkedin/answer/a563309); YouTube thumbnails (https://support.google.com/youtube/answer/72431) and banner (https://support.google.com/youtube/answer/10456525); Pinterest ad specs (https://help.pinterest.com/en/business/article/pinterest-product-specs).

The Facebook figures are for Pages, the profiles that businesses and organisations use; we could not confirm Facebook’s figures for personal profiles or feed photos. LinkedIn’s 400 × 400 is a minimum, not a target. Pinterest’s figure comes from its advertising specifications; its guide to designing an ordinary Pin offers shapes but no pixel size. For Instagram Stories and Reel covers, and for photos posted on X, we could not read an official figure, so none is given.

Passport and visa photo sizes in pixels

Online passport and visa applications describe the photo in pixels, and most also set a limit in kilobytes. The table lists the pixel rules we could confirm on each official page, with the file-size limit alongside. Reaching a KB limit without ruining the photo is a separate problem with its own guide: how to compress a photo to 20 KB, 50 KB, 100 KB or 200 KB for online forms, which covers exam and job portals too.

Sources: US Department of State (https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/photos.html), as published on its photo requirements page, read through the Internet Archive copy of 30 December 2025 because the live page blocks automated checks; GOV.UK (https://www.gov.uk/photos-for-passports/rules-for-digital-photos); the Passport Seva instruction PDF (https://assets.ctfassets.net/xxg4p8gt3sg6/65N7mZz0hfj57DM1VlnLA2/284bfc9bd711eda8a8564dad5019cc70/PASSPORT_SEVA_PHOTO_UPLOAD_INSTUCTIONS.pdf), which we could not trace to the page on passportindia.gov.in that links to it; DGIP (https://www.dgip.gov.pk/eServices/online-passport.php); IRCC (https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/citizenship-application-photograph-specifications/grant-online.html); Government of Canada passport photos (https://www.canada.ca/en/immigration-refugees-citizenship/services/canadian-passports/photos.html); VFS Global (https://www.vfsglobal.com/one-pager/belgium/iran/english/pdf/photo-specification.pdf), which covers one country and one set of visa centres only, since Schengen countries do not publish one shared digital rule.

630 × 810 and 420 × 540 are both 7:9, the same proportions as a 35 × 45 mm printed photo, so a crop made for one fits the other. Pixel size is only part of an ID photo’s rules, though: these pages also set out head size, background, expression and lighting, and those decide acceptance as much as the pixels do. A resizing tool can make the pixels right; it cannot check your face, so read the official page before you submit.

Pixel size and file size are different things

A photo’s file size in kilobytes is not its image size. We measured a real portrait resized to 1600 × 2000 pixels (3.2 megapixels) and saved as JPG with MozJPEG, the encoder our image tools use: 131.6 KB at quality 50, 217.2 KB at quality 75 and 893.0 KB at quality 95. The pixel count never changed, yet the file at quality 95 was nearly seven times the size of the one at quality 50.

Pixels matter too, though less than you might expect. The same portrait at 600 × 600 came to 37.6 KB at quality 75, and at 1200 × 1200, four times the pixels, 111.7 KB: about three times the size, not four. When an upload form sets a KB limit, set the right pixel size first, then a quality that lands under the limit; the KB compression guide goes through it step by step. If the problem is the format rather than the size, such as an iPhone HEIC file a website refuses, the Image Converter turns it into a JPG or PNG.

Upscaling: why software cannot invent missing detail

Making a photo larger is called upscaling. Ask an editor for twice the width and height and it creates four pixels for every one it had, working out each new pixel’s colour as a weighted average of its neighbours. The filter (bicubic, or Lanczos, the Image Resizer’s default) changes how smooth or crisp the result looks, but none adds information. A face that was 40 pixels wide is still a 40-pixel face, now spread over 80 pixels, with softer edges. That is why a small image printed large looks blurry, and why the Image Resizer shows a warning before it enlarges: the file gets bigger, the detail does not.

AI upscalers work differently. They are neural networks trained on large collections of paired small and large images, so they learn what fine detail usually looks like: the texture of hair, skin, fabric, brick or leaves. Given your small photo, they paint in detail of that kind where it seems to belong. The result can look sharp, but the new detail is a prediction, not a recovery: letters can change shape, faces can drift towards a generic look, and patterns appear that were never there. For a decorative landscape print that may be acceptable; for an ID photo, a document or anything that must show how something really looked, it is not. The Image Resizer does not use AI.

Screen colour and print colour

A screen makes colour by emitting red, green and blue light, and almost every photo and web image describes its colours in a standard called sRGB. Some recent phones capture a wider range, Display P3, which the Image Converter maps to sRGB when it saves, so colours look the same in any browser. A printer works the other way round: cyan, magenta, yellow and black ink (CMYK) on paper that reflects light, which cannot reproduce some of the brightest, most saturated colours a screen can show. That is why prints often look darker and flatter than a phone at full brightness. For photo prints, send an sRGB JPG unless your printer asks for something else, and let it do the conversion. Which of JPG, PNG and PDF suits print and documents is covered in PDF vs JPG vs PNG.

Worked example: one phone photo, three destinations

Take a head-and-shoulders portrait taken on a 12-megapixel phone, held upright, against a plain light wall. The file is 4032 × 3024 pixels turned on its side: 3024 wide by 4032 tall, a 3:4 shape. We want a 7 × 5 inch print for a relative, an Instagram portrait post, and a photo for a UK passport application.

1. A 7 × 5 inch print at 300 DPI

• Pixels needed: 5 in × 300 by 7 in × 300 = 1500 × 2100 (3.15 megapixels).
• Shape: the print is 5:7, or 0.714; the photo is 3:4, or 0.750. The photo is slightly too wide, so the crop comes off the sides.
• Crop: keep the full height of 4032 and make the width 4032 × 5 ÷ 7 = 2880. That removes 144 pixels of width, 72 from each side if centred, and keeps 95.2% of the photo.
• Resize: scaling 2880 × 4032 by 1500 ÷ 2880 = 0.521 gives exactly 1500 × 2100; tag it 300 DPI. The crop alone already had 4032 ÷ 7 = 576 pixels per inch, so there is detail to spare.
• For a landscape print the numbers swap: 4032 × 3024 cropped to 4032 × 2880, then resized to 2100 × 1500.

2. An Instagram portrait post at 4:5

• Pixels: Instagram keeps photos up to 1080 wide, so a 4:5 post is 1080 × 1350.
• Shape: 4:5 is 0.800 and the photo is 0.750, so this time the photo is too tall and the crop comes off the top and bottom.
• Crop: keep the full width of 3024 and make the height 3024 × 5 ÷ 4 = 3780. That removes 252 rows and keeps 93.75% of the photo.
• Resize: 3024 ÷ 1080 = 2.8, and 3780 ÷ 2.8 = 1350, so the crop scales exactly to 1080 × 1350 (1.46 megapixels, about an eighth of the original).
• Or skip the crop: 3:4 is inside Instagram’s stated range, so the uncropped photo can go up at 1080 × 1440. The 4:5 crop is a choice about framing, not a requirement.

3. A UK passport photo

• Rule: GOV.UK asks for at least 600 × 750 pixels and a file between 50 KB and 10 MB, plus rules on head position, background and expression that you check yourself.
• Crop: the 3024 × 3780 crop from step 2 is already 4:5, the same shape as 600 × 750, so it can be reframed around the head and reused.
• Resize: the Image Resizer’s UK passport preset uses 900 × 1125, one and a half times the minimum on each side.
• File size: this is where the minimum bites. On our test portrait, exactly 600 × 750 pixels at JPG quality 75 came to 46.1 KB, under the 50 KB floor; at quality 85 it was 70.5 KB. Check the result before you upload.

What size should an image be for a website or email?

For the web, DPI is irrelevant and pixels and kilobytes are everything. The web presets in the Image Resizer are a reasonable starting point: 2400 pixels on the long side for a full-width image on large high-density screens, 1600 for a photo inside a web page, 1200 for an email attachment, and 600 wide for a picture inside an email newsletter column. Anything much larger slows the page without looking better, which is why the next step after resizing is usually compressing. More guides on converting, compressing and sending files are collected in Files and PDFs.

Frequently asked questions