Why buy more fabric than the pattern says?

Washable fabrics shrink in their first wash. If you buy exactly the pattern amount and pre-wash it, you will end up short. Buying the grossed-up amount means the post-wash yardage matches what your pattern needs.

How is the pre-wash amount calculated?

It divides the required yardage by (1 minus the shrinkage fraction). For 3 yards needed at 5 percent shrinkage, you need 3 divided by 0.95, about 3.16 yards, so the fabric still measures 3 yards after washing.

What shrinkage percentage should I use?

Quilting cotton typically shrinks 2 to 4 percent, flannel and wool 5 to 10 percent, and linen 3 to 5 percent. When the bolt or manufacturer states a figure use that; otherwise pre-wash a test swatch and measure before and after.

Does shrinkage apply to width too?

Yes, fabric usually shrinks in both length and width. This calculator adjusts length yardage, which is what patterns specify. If your layout is width-critical, pre-wash a swatch and check the usable width after washing.

Should I always pre-wash?

Pre-washing is wise whenever the finished item will be laundered, especially for mixed fabrics in one project that may shrink at different rates. Pre-washing each fabric first prevents puckering and distortion after the first wash of the finished piece.

Fabric Shrinkage Calculator

If you pre-wash your fabric, buying exactly the pattern yardage leaves you short because the fabric shrinks before you cut. This calculator grosses up your requirement so that, after washing, the shrunk fabric still meets the pattern.

How it works

Shrinkage removes a percentage of the length, so the amount you must buy is the required amount divided by the fraction that survives washing:

buy = required / (1 − shrinkage%)
lost = buy − required

For example, 3 yards required at 5 percent shrinkage needs 3 / 0.95 ≈ 3.16 yards. Note that you divide rather than simply adding 5 percent: adding 5 percent (3.15 yards) is slightly too little, because the 5 percent loss applies to the larger pre-wash length, not the smaller required length.

Tips and example

Flannel commonly shrinks 8 to 10 percent, so a quilt backing needing 4 yards could require 4 / 0.90 ≈ 4.44 yards — nearly half a yard more. Always round up to the nearest quarter yard at the cutting counter, and pre-wash a test swatch to confirm the manufacturer’s stated shrinkage before committing to a large cut. When several fabrics share one project, pre-wash each separately so they shrink before being sewn together.