Fabric Shrinkage Calculator
Cut length that survives the first wash.
Calculate the cut length needed to end up at a finished size after shrinkage, and the extra yardage to buy for pre-washing.
Cotton 3-5%, linen 4-10%, wool variable, most synthetics near zero. Knits shrink more than wovens.
Cut this length
37.89"
1.05 yd · 1.89" extra
Shrinkage is a proportion of the original, so recovering a finished length divides rather than subtracts. Subtracting the percentage — the intuitive move — leaves you short, and the gap widens as the percentage rises. Pre-wash exactly as the finished item will be washed.
How the Fabric Shrinkage Calculator works
Shrinkage is a proportion of what you started with, which means recovering a finished length is a division rather than a subtraction. Ten percent shrinkage on a 36 inch finished piece needs 40 inches of fabric, not 39.6 — and the four-tenths of an inch difference between those two answers is exactly the sort of gap that turns a hem into a problem.
Also known as: prewash allowance calculator · shrinkage allowance calculator
Why shrinkage divides rather than subtracts
Shrinkage is quoted as a percentage of the fabric you started with, not of the fabric you end up with. If a cloth shrinks 10%, then a cut length L becomes 0.9L after washing. To finish at 36 inches you therefore need L such that 0.9L = 36, which is 36 divided by 0.9, or 40 inches.
The intuitive move — take 36 and add 10% — gives 39.6, and it is wrong every time. The error is small at low percentages and grows quickly: at 5% it is under a fifth of an inch on a yard, at 15% it is nearly three quarters of an inch, and on a full-length curtain drop at 10% it is over an inch.
The same asymmetry appears anywhere a percentage is applied and then reversed, which is why the reverse-VAT and reverse-fee calculators on this site work the same way.
A worked example
A linen with 8% shrinkage, and a finished curtain drop of 90 inches. The cut length is 90 divided by 0.92, which is 97.8 inches. Adding 10% instead would have given 99 — in this direction it happens to be generous, because adding a percentage to a larger number overshoots — but subtracting 8% from the finished length, the more common error, would have given 82.8 and a curtain seven inches short of the floor.
Across three drops, the difference between the correct 97.8 and the naive 82.8 is 45 inches of fabric, or one and a quarter yards.
Where the answer misleads
Shrinkage is rarely equal in both directions. Wovens usually shrink more along the length than across the width, because the warp is under tension during weaving and finishing and relaxes when washed. Knits shrink more still, and often in width as well.
A single figure also hides the fact that most shrinkage happens on the first wash and a little more on the next few. Residual shrinkage after a proper pre-wash is usually under one percent, but for a fitted garment in cotton it is worth washing twice before cutting.
Finally, pre-washing only helps if you wash the fabric the way the finished item will be washed. Pre-washing cold and then laundering the garment hot moves the shrinkage to exactly where you did not want it.
Frequently asked questions
How much do fabrics shrink?
Cotton typically 3 to 5% and sometimes more on the first hot wash, linen 4 to 10%, wool variably and unpredictably, and most synthetics almost nothing. Knits shrink more than wovens, and length more than width.
What is the formula?
Cut length equals finished length divided by one minus the shrinkage as a decimal. For 10%, divide by 0.9. Subtracting 10% instead gives an answer that is short by about 1% of the finished length, and it gets worse as the percentage rises.
Should I pre-wash?
For anything washable that will be washed, yes — wash and dry it exactly as the finished item will be treated. It is the only way to move the shrinkage before you cut rather than after you sew, and it also removes sizing that can affect how the fabric handles.
Does fabric shrink again after the first wash?
Usually a little, called residual shrinkage, typically under 1% after a proper pre-wash. For a fitted garment in cotton it is worth washing twice before cutting, since the second wash catches most of what the first left behind.
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