Quilt Fabric Yardage Calculator

How to Calculate Quilt Fabric Yardage

A quilt top is a grid of blocks, each cut oversized so the seam allowance can be sewn away. Fabric comes off a bolt of fixed width, so the question that decides what you buy is not “how many square inches” but “how many squares fit across the bolt”.

The formulas

Cut block size = Finished block + (2 × Seam allowance) Blocks across = Floor(Quilt width ÷ Finished block) Blocks down = Floor(Quilt length ÷ Finished block) Blocks per color = Total blocks ÷ Colors, rounded up Squares per row = Floor(Usable fabric width ÷ Cut block size) Rows to cut = Blocks per color ÷ Squares per row, rounded up Fabric per color = Rows × Cut block size × (1 + Waste %), then ÷ 36 for yards

Why area alone under-buys

Dividing total square inches by the fabric width is the intuitive method, and it comes up short. Cut 12½" squares from 42" of usable width and only three fit across. The leftover 4½" strip is too narrow for a fourth, so it is gone before the waste factor is even applied.

No percentage fudge recovers this, because the loss depends entirely on how the cut size divides into the bolt. A 10½" block gets four across with 0 wasted. Bump it to 12½" and you lose more than a tenth of every yard. That is the difference between a quilt and a quilt with one block missing, which is why this calculator counts rows instead.

Standard seam allowances

A quarter inch is the quilting default and what nearly every published pattern assumes. Some use ⅜" or ½". Check before cutting, since the seam allowance changes the cut size of every block in the quilt.

Fabric width

Quilting cotton is sold as 44" wide, but the selvages are unusable and the edges are rarely square, so this works to 42" usable. If your fabric is genuinely wider, or you are using 108" wide backing fabric, you will need less than this says.

Waste and shrinkage

The waste factor covers cutting errors, squaring up, and pre-wash shrinkage, which runs 3–5% on quilting cotton. Ten percent is a sensible default. Push it to 20% for directional prints or anything that needs fussy cutting to centre a motif, because matching a print costs fabric that plain yardage never does.