Quilt math · Calculator
Shrinkage and pre-washing: how much extra to buy
Washed fabric comes out shorter and narrower. If you pre-wash, buy a little more: here’s how much, worked out to the ⅛ yard.
The short answer
Buy enough that what’s left after washing is what you need: what you need ÷ (100% − the shrinkage). For 4 yd of fabric that shrinks 3%, buy 4⅛ yd. A 42″ width washes down to about 40⅝″.
Work out yours
Free · no accountNeed 4 yd after washing
Shrinks 3% in length and width
148½″ dry shrinks to the 144″ you need. Up to the next ⅛ yd.
42″ on the bolt, less 3%, down to the ⅛″.
Its 40″ between trimmed selvages, washed. The backing calculator uses this.
In Quarter Inch, turn on “I pre-wash my fabric” and every yardage, strip and backing is worked out from the washed width and length.
Start a quiltSame sums as the app: @quarterinch/cutting, dryLength and washedWidth · lengths up, widths down, to the ⅛″
Should you pre-wash quilt fabric?
Quilters disagree, and both ways make good quilts. What matters is choosing before you buy, because washed fabric is smaller.
- Pre-wash when a fabric might bleed (deep reds, navies, hand-dyes), when you’re mixing fabrics that may shrink differently, or when the quilt will be washed often and should keep its size.
- Don’t pre-wash when you want the soft, crinkled look that comes from fabric and batting shrinking together after quilting, or when you’re using precuts: small pieces fray and shrink out of true in the wash.
How much does quilting cotton shrink? One quilting site’s shrink tests found good fabrics shrank about 2% in length and width, and poorer ones up to 6%. The only way to know yours is to test it.
How it’s worked out
Washing takes a share off the length and the width. To be left with what you need, divide by what’s left: at 3%, buy what you need ÷ 0.97, then round up to the next ⅛ yd.
| Fabric you need, washed | 4 yd (144″) |
|---|---|
| It shrinks 3%, so 97% of what you buy is left: 144″ ÷ 0.97 | 148½″ |
| Up to the next ⅛ yd | 4⅛ yd |
| And the width: 42″ less 3%, down to the ⅛″ | 40⅝″ |
The width matters as much as the length. Strips are cut across the fabric, so a narrower width can mean an extra strip, and a backing can need an extra width: a queen backing of 42″ fabric takes 8¼ yd unwashed and 8½ yd washed at 3%.
How much extra to buy
| You need | Buy at 2% | Buy at 3% | Buy at 5% |
|---|---|---|---|
| 1 yd | 1⅛ yd | 1⅛ yd | 1⅛ yd |
| 2 yd | 2⅛ yd | 2⅛ yd | 2⅛ yd |
| 3 yd | 3⅛ yd | 3⅛ yd | 3¼ yd |
| 4 yd | 4⅛ yd | 4⅛ yd | 4¼ yd |
| 6 yd | 6⅛ yd | 6¼ yd | 6⅜ yd |
| 8 yd | 8¼ yd | 8¼ yd | 8½ yd |
Test your own fabric
- Cut a 10″ square, straight on the grain. Draw around it on paper.
- Wash and dry it the way you’ll wash the quilt, then press it.
- Measure it again. If it’s 9¾″, it shrank 2.5%: use 3% in the calculator. Measure both ways: fabric often shrinks more along its length than across.
Batting can shrink too: see batting sizes, and for the fabric’s width, width of fabric explained.
Questions
Short answers.
Something else? A real person replies.
hello@quarterinch.app
Should I prewash quilt fabric?
It’s your choice. Pre-wash fabrics that might bleed, or when the quilt must keep its size. Skip it for precuts, or for a crinkled, vintage look after washing.
How much does quilting cotton shrink?
Often about 2%, and up to 6% for poorer fabric. Test a 10″ square to know yours.
How much extra fabric should I buy to prewash?
About the shrinkage, rounded up: for 4 yd at 3%, buy 4⅛ yd.
Should I prewash precuts?
No. Jelly roll strips, charm squares and layer cakes fray and shrink out of shape in the wash. Use them as they come.
Sources
We checked every fact above against these pages on , and we update this guide when they change. Spotted something out of date? Write to hello@quarterinch.app.
- Fabric Shrinkage All-About-Quilts.com