Prewashing quilt fabric and the shrinkage math
Updated 2026-07-13
The quick answer: quilting cotton typically shrinks 2–5% on first wash, mostly along the length. If you prewash — or if you buy for a quilt that will be washed — add about 5% to your yardage and round up to the nearest 1/4 yard. For a 5-yard backing that means buying 5 1/4 to 5 1/2 yards.
Should you prewash at all?
There’s no single right answer — there’s a consistent one:
Prewash when:
- The quilt mixes fabrics from different sources or eras (they’ll shrink at different rates)
- You’re using saturated reds, purples, or navies that might bleed
- The recipient will machine-wash and dry the quilt hard (kids, pets, daily use)
- You’re sensitive to sizing and finishing chemicals
Skip prewashing when:
- You want the classic crinkle: washing the finished quilt shrinks the cotton batting and fabric together, producing that antique pucker
- You’re working with precuts — charm squares and jelly roll strips distort and fray badly in a wash, and their pinked edges are cut to exact size before shrinkage
- Everything in the quilt is the same line of modern quilting cotton (it will shrink uniformly)
The one real rule: don’t mix. Prewashed blocks sewn next to unwashed blocks will shrink differently at the first wash and pucker unevenly along the seams.
The shrinkage numbers
| Fabric | Typical shrinkage |
|---|---|
| Quilting cotton | 2–5% |
| Flannel | 5–10% (buy 10% extra, always) |
| Cotton batting | 3–5% |
| Polyester batting | ~0–1% |
| Voile / lawn | 2–3% |
Lengthwise shrinkage usually exceeds crosswise — a prewashed yard can come back 34“–35“ long. That matters most for backing: a backing cut with only 2“ of overhang before washing may not have 2“ after.
The buying math
If a project needs Y yards and the fabric shrinks at rate s, buy Y ÷ (1 − s). In practice quilters simplify to add the percentage and round up:
| Needed | +5%, rounded to 1/4 yd |
|---|---|
| 1 yd | 1 1/8 → 1 1/4 yd |
| 3 yd | 3.15 → 3 1/4 yd |
| 5 yd | 5 1/4 → 5 1/4 yd |
| 8 yd (king backing) | 8.4 → 8 1/2 yd |
Flannel: use 10% and round up a full half yard.
If you do prewash
Wash on warm, dry on medium — the point is to force the shrinkage now, gently. Snip a small triangle off each corner first to reduce fraying, or serge/zigzag the cut edges. Press with starch or sizing afterwards to restore the body the wash removed; blocks piece more accurately with a little stiffness.
When you’re figuring what a quilt needs before the shrinkage question, the free backing and fabric yardage calculators give you the base number to add your percentage to.