# Wood Shrinkage & Seasonal Movement Calculator Model exact wood shrinkage and seasonal dimensional changes based on relative humidity, temperature, and wood species type. --- - **Canonical URL:** https://dothecalculation.com/calculators/wood-shrinkage-radial-calculator - **Category:** Hobbies & Leisure Utilities - **Publisher:** Do The Calculation (https://dothecalculation.com) - **Cost:** Free, no account or sign-up required - **Privacy:** Runs entirely in the browser; inputs are never sent to a server - **Methodology:** https://dothecalculation.com/methodology --- ## Calculate wood shrinkage and seasonal movement Model wood movement and dimensional stability based on relative humidity, temperature, wood species, and grain direction. - Equilibrium Moisture Content (EMC) solver - Anisotropic wood shrinkage coefficients - Radial and Tangential grain models ## Equilibrium Moisture Content (EMC) and Environmental Physics Wood is a hygroscopic material, meaning it constantly absorbs and releases moisture to stay in equilibrium with the surrounding atmosphere. The moisture content of wood at equilibrium is called the Equilibrium Moisture Content (EMC). EMC is determined by the relative humidity (RH) and temperature of the air. To model EMC mathematically, the USDA Forest Products Laboratory uses a complex equation based on Hailwood-Horrobin models: \(EMC = \frac{1800}{W} \left[ \frac{kh}{1-kh} + \frac{k_1 kh + 2 k_2 k_1 k^2 h^2}{1 + k_1 kh + k_2 k_1 k^2 h^2} \right]\), where \(h\) is relative humidity as a fraction, and \(W, k, k_1, k_2\) are temperature-dependent coefficients. Solving this formula allows woodworkers to predict wood moisture changes when moving lumber between different climates. ## Radial vs. Tangential Wood Movement Dynamics Wood is anisotropic, meaning its physical properties differ depending on grain direction. Wood shrinks very little longitudinally (along the length of the tree), moderately radially (across the growth rings), and most significantly tangentially (parallel to the growth rings). Tangential shrinkage is typically 1.5 to 2.0 times greater than radial shrinkage. The dimensional change equation is: \(\Delta D = D_i \times C \times \frac{\Delta MC}{FSP}\), where \(D_i\) is the initial board width, \(C\) is the species shrinkage coefficient (radial or tangential), \(\Delta MC\) is the change in wood moisture content, and \(FSP\) is the Fiber Saturation Point (assumed to be 30% MC). Below the FSP, water leaves the wood cell walls, causing shrinkage. Above the FSP, additional moisture does not affect dimensions. ## How to Use This Calculator Enter your board width, select a wood species, and choose whether you're entering moisture content (MC%) directly or relative humidity (RH%) plus temperature. Enter your initial and target conditions and select radial or tangential grain orientation. The calculator returns the resulting dimensional change and new board width range. ## Worked Example: A 10-Inch Red Oak Board Drying Out With the calculator's defaults — a 10-inch-wide red oak board, moisture content mode, drying from 12% MC to 6% MC, tangential grain — the board is expected to shrink by about 0.172 inches, narrowing from 10 inches to roughly 9.83 inches. Red oak's tangential shrinkage coefficient (8.6%) is applied against the 6-percentage-point moisture drop relative to the 30% fiber saturation point, illustrating why a solid red oak tabletop can visibly narrow between a humid summer and a dry, heated winter if it isn't allowed room to move. ## Related Calculators For estimating total lumber cost and board feet alongside movement, see the [Woodworking Wood Movement & Board Foot Calculator](/calculators/woodworking-board-foot-movement-calculator). Filling the gap left by seasonal movement with epoxy? The [epoxy resin calculator](/calculators/epoxy-resin-calculator) sizes the resin batch for that void — see the [epoxy resin guide](/blog/hobby/epoxy-resin-guide) for why volume ratios and weight ratios are never the same number. ## Frequently asked questions ### What is the Fiber Saturation Point (FSP)? The moisture content (around 30%) where wood cell walls are completely saturated but cell cavities are empty of liquid water. ### Why does wood shrink more tangentially than radially? Growth rings act like arches, meaning tangential cells buckle and contract more than radial cells during drying. ### How does humidity affect wood movement? High humidity raises wood moisture content, causing expansion. Low humidity dries wood, causing shrinkage. ### What is flat-sawn vs quarter-sawn wood? Flat-sawn boards show tangential grain on their faces (maximizing movement), whereas quarter-sawn boards show radial grain (minimizing movement). ### What is a typical wood moisture content range? Indoor furniture usually stabilizes between 6% and 8% moisture content, while outdoor wood ranges from 12% to 15%. ### How does temperature impact wood moisture? Higher temperatures speed up moisture exchange and slightly lower the equilibrium moisture content for a given relative humidity. ### Which wood species is most stable? Teak and Mahogany have very low shrinkage coefficients, making them extremely stable. Oak and Beech move much more. ### How do you prevent wood movement? Wood movement cannot be stopped. You must design joints (like mortise and tenons with slots) that allow the wood to expand and contract. ### What is anisotropy? The characteristic of exhibiting different physical properties in different directions. ### Does paint stop wood movement? No. Paint and finishes slow down the rate of moisture exchange, but do not stop wood from eventually reaching equilibrium. ### Should I enter relative humidity or moisture content if I have a moisture meter reading? Use the moisture content (MC%) input mode directly — a pin or pinless moisture meter reading is already the wood's actual MC, so converting through relative humidity would add unnecessary approximation error. ### How much wider will a quarter-sawn board be compared to flat-sawn under the same humidity swing? Quarter-sawn (radial) boards typically move about half as much as flat-sawn (tangential) boards of the same species and width, since radial shrinkage coefficients run roughly 1.5 to 2 times lower than tangential ones. ## Related concepts - **Equilibrium Moisture Content (EMC)** — The stable moisture level of wood in a given humidity and temperature. - **Tangential and Radial shrinkage** — Directional shrinkage percentages from green to oven-dry. - **Joinery tolerance design** — Engineering expansion gaps in traditional wood joints. ## Related guides - [Understanding Calculator Formulas: How DTC Turns Inputs into Results](https://dothecalculation.com/blog/site-guides/understanding-calculator-formulas) — Understand how Do The Calculation formulas are presented, what the explanation blocks mean, and how to verify calculator logic before using a result in a real decision. ## Related calculators - [Geocaching Coordinates Distance & Bearing Solver](https://dothecalculation.com/calculators/geocaching-distance-bearing-calculator) — Solve the exact distance and compass bearing between two GPS coordinates, or project a new waypoint using the Haversine formula. - [Model Rocket Aerodynamic Drag & Apogee Calculator](https://dothecalculation.com/calculators/model-rocket-drag-apogee-calculator) — Simulate rocket flight to calculate peak altitude, apogee, drag coefficient, and maximum velocity using numerical integration. - [Woodworking Wood Movement & Board Foot Calculator](https://dothecalculation.com/calculators/woodworking-board-foot-movement-calculator) — Calculate lumber board feet and seasonal wood expansion or contraction based on wood species and relative humidity levels. - [Crochet Blanket Size & Yardage Calculator](https://dothecalculation.com/calculators/crochet-blanket-dimensions-calculator) — Calculate the yarn yardage, skein count, and finished blanket weight based on your stitch density, gauge, and yarn class. - [Photography Exposure Value & Reciprocity Calculator](https://dothecalculation.com/calculators/photography-exposure-value-calculator) — Calculate Exposure Value (EV) and EV100, and compensate for film reciprocity failure during very long exposures in photography. - [RC Battery C-Rating & Continuous Current Calculator](https://dothecalculation.com/calculators/rc-battery-c-rating-calculator) — Calculate safe continuous discharge limits, average throttle current, and expected flight runtime for your LiPo battery. --- _This calculator is for educational and planning purposes. Always verify measurements, conversions, and material requirements before making purchases or physical builds._ --- _Source: [Do The Calculation](https://dothecalculation.com/calculators/wood-shrinkage-radial-calculator). Quote freely with attribution and a link to this page._