Free Wood Movement Calculator

Last updated: November 3, 2026

Quick answer: Wood does not sit still: it swells across the grain when the air gets damp and shrinks when the air dries out, and a tabletop that fit in July can split a joint or jam a drawer in January. This free wood movement calculator predicts that change before you build: enter your panel width, species, cut (flatsawn or quartersawn), and the moisture-content swing between your damp and dry seasons, and it returns the movement in inches and millimetres, the new width, and the gap to leave — plus the reverse answer, the largest moisture swing a gap you already have can absorb. On the defaults (a 36-inch flatsawn white ash panel, 12% down to 6% moisture), the panel shrinks 0.59 inches (15.0 mm), to 35.41 inches. Everything runs in your browser; no signup. Coefficients are typical published values — individual boards vary — so use the result as a planning allowance, and always leave a little more room than the number says.

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How to Use the Wood Movement Calculator

1. Enter the panel width across the grain in inches — the dimension that moves. Wood moves almost entirely across the grain (width), barely along the grain (length), so measure edge to edge across the face grain, not the length of the board. For a glued-up panel, use the full panel width; for a single board, its width.
2. Pick the species and the cut. The coefficient is the published dimensional-change value: how much the wood changes per inch of width per 1% change in moisture content. Flatsawn (tangential) coefficients run roughly twice the quartersawn (radial) ones — white ash is 0.00274 flatsawn against 0.00169 quartersawn — which is why two panels of the same species and width can move very differently. If your species is not listed, choose the custom coefficient and enter a published value for it.
3. Enter the moisture content of your damp season and your dry season as percentages. Climate-controlled houses typically swing 3 to 4 points in a year; unconditioned shops and cabins can swing far more. If you own a moisture meter, use your own readings (highest in the wet season, lowest in the dry season); otherwise the 12% to 6% defaults are a reasonable indoor planning swing. The formula only holds below the fiber saturation point (about 28%), which is why the inputs stop there.
4. Optionally enter a gap you already have — the clearance in an existing frame, groove, or drawer opening. The reverse solver tells you the largest moisture swing that gap can absorb, so you can judge whether an existing fit will survive your seasons or bind the first winter.
5. Press Calculate wood movement and read the movement (with its direction: shrinkage on drying, swelling on wetting), the new width, and the gap to leave. Design to the gap, not to the current fit: a panel glued tight into a frame at summer moisture has nowhere to go when it swells, and a panel fitted tight in winter will show a gap by summer either way — the calculator tells you how big that gap will be.

Why Use Our Wood Movement Calculator?

• Species and cut, not one generic number — movement depends on both, and the ranking tools that ask only for width silently assume one coefficient. This page carries published coefficients for 7 species in both cuts (American beech flatsawn, at 0.00431, moves more than twice as much per point as eastern red cedar quartersawn, at 0.00106), plus a custom coefficient for anything unlisted.
• Direction, not just distance — drying shrinks, wetting swells, and the fix differs: a shrinking panel needs room to pull in without opening a joint, a swelling panel needs room to grow without splitting a frame. The result names the direction so the allowance goes in the right place.
• Gap to leave, stated as a design number — most movement tools return the movement and leave the joinery decision to you. This page converts it directly into the clearance to design around, split across both sides for a centered panel, which is the number a frame, groove, or drawer actually needs.
• Reverse solver for existing fits — when the frame already exists, the question flips: how much moisture swing can this gap take? Enter the gap and the calculator answers in moisture points, so you can check an old dresser, a bought tabletop, or a floor gap against your seasons before it binds or opens.
• Honest about the limits — the formula holds only below the fiber saturation point, coefficients are typical values that vary 10–20% board to board, and the calculator predicts size change only, not cupping, checking, or twisting. Those limits are stated on the page, not buried, because a movement number used as a guarantee is worse than no number.

Common Use Cases

• A 36-inch flatsawn white ash tabletop, indoor seasons: Moisture 12% down to 6% (6 points): movement = 36 x 0.00274 x 6 = 0.59 inches, shrinking to 35.41 inches. Leave at least 0.59 inches of total clearance for the top — about 0.30 inches per side if it is centered — or the top will either split its joints when it shrinks or jam the aprons when it swells back. A top fitted tight in summer has nowhere to go by winter.
• The same top, quartersawn instead: Quartersawn white ash coefficient 0.00169: movement = 36 x 0.00169 x 6 = 0.37 inches, to 35.63 inches. Same species, same seasons, 0.22 inches less movement — the reason quartersawn stock is worth its premium for wide tabletops and door panels, and the reason the cut selector matters more than most builders expect.
• A beech drawer front in a dry winter: A 12-inch American beech drawer front, flatsawn (0.00431 — one of the highest coefficients), drying from 10% to 6% (4 points): movement = 12 x 0.00431 x 4 = 0.21 inches. That is enough to open a visible gap at the drawer sides or, fitted tight in summer, to bind in winter. Beech fronts need the full calculated clearance, not a friction fit.
• Checking an existing frame before it binds: A 24-inch flatsawn red maple panel sits in a frame with 0.25 inches of total gap. Reverse solver: 0.25 / (24 x 0.00289) = 3.6 points of moisture swing. The house swings 6 points between seasons, so the panel will bind on the wet swing and show a gap on the dry one — the frame needs widening, or the panel needs trimming, before the next season decides for you.

Wood Movement Calculator vs Alternatives

• Single-number movement tools (the small tools ranking today): KM Tools, WoodWorkCalc, Calcimator, and the other ranking calculators compute the same formula correctly — width x coefficient x moisture change — and stop at the movement number. They do not carry a species x cut table you can trust (most ask you to type the coefficient yourself), do not state the gap to leave, and do not run the reverse solver for an existing fit. Use them to check a number you already have; use this page to get the number and the design decision together.
• Woodworking guides (the publisher pages on page 2): Fine Woodworking's Shrinkulator write-up and Popular Woodworking's movement guide are where the coefficients and the formula come from — this page's table is drawn from that published tradition. But a guide is not a calculator: it gives you the chart and the worked example and leaves the arithmetic for your panel to you, by hand, every time. This page turns the same published numbers into your panel's answer in one run.
• Rules of thumb (the forum answers): The forum rule — 'allow 1/8 inch per foot of width' — is roughly right for average species at average swings (1/8 inch per foot is 0.0104 per inch of width, close to a mid-range coefficient at a 4-point swing), and for a small project it is enough. On a wide panel, a high-movement species like beech, or a big seasonal swing, the rule is off by enough to split a joint: beech flatsawn at a 6-point swing moves 0.026 inches per inch of width, more than double the rule. The calculator replaces the rule with your species, your cut, and your swing.

If you only need one movement number checked, any of the ranking tools will compute it. If you need the species and cut accounted for, the gap to design around, and the reverse check on a fit that already exists, you need those three answers together — and that is the job this page does.

Frequently Asked Questions