Fabric Shrinkage Allowance Calculator
Buy enough fabric to survive pre-washing by adding a shrinkage allowance to the length and width you need.
How it works
Buy length = needed length ÷ (1 − lengthwise shrink%) · Buy width = needed width ÷ (1 − widthwise shrink%) · round the length up to the next ¼ yd
Natural fibers relax and shrink the first time they are washed, so a garment cut from unwashed fabric can come out a size too small after its first laundering. To guarantee the finished dimension you divide by one minus the shrinkage rate rather than simply adding the percentage — the two are not the same once shrinkage is more than a few percent. Pre-washing the fabric before cutting locks the size in and is why this allowance matters most for cottons, linens and denim.
Worked example
You need 3 yd after washing and expect 5% lengthwise shrinkage. Buy 3 ÷ (1 − 0.05) = 3.16 yd, rounded up to 3.25 yd at the cutting counter — about a sixth of a yard of insurance. Widthwise, a 44 in requirement at 3% shrink needs fabric starting at 44 ÷ 0.97 = 45.4 in.
Frequently asked questions
Why divide instead of just adding the percentage?
Shrinkage is measured against the original size, so recovering a finished length means working backward. Adding 5% to 3 yd undershoots; dividing 3 by 0.95 gives the true 3.16 yd that shrinks back down to exactly 3. The gap grows as shrinkage rises.
How much does fabric typically shrink?
Cotton and linen commonly shrink 3–5% but can reach 10% for loose weaves or flannel; denim 5–10%; wool varies and can felt if washed hot. Synthetics like polyester barely move. Check the bolt or test-wash a swatch when precision matters.
Should I pre-wash before cutting?
Yes, whenever the finished item will be washed. Pre-washing (and drying the same way you will launder the garment) shrinks the fabric up front so your cut pieces stay true to size — and it removes sizing and excess dye at the same time.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.