Rag Quilt Calculator: Square Size, Count and Flannel Yardage

Calculator

Turn on JavaScript to use the calculator, or use the baby and throw amounts in the flannel rag quilt pattern.

Cross-section of a rag block with flannel front and back and a smaller batting square between them — One block in cross-section: front and back cut 8 inches, batting cut 6 inches, seam lines (dashed) ½ inch in from each edge. The batting stays out of the seam allowance, which is what lets it fray.

How the math works

What	Formula	8 in squares, ½ in seams, 5 × 6
Finished block	cut − 2 × seam	8 − 1 = 7 in
Finished quilt	blocks × finished block + 2 × seam (the ragged outer edge)	5 × 7 + 1 = 36 in by 6 × 7 + 1 = 43 in
Squares per layer	across × down	30
Squares per strip	40 ÷ cut, rounded down	5
Strips	squares ÷ squares per strip, rounded up	6
Yardage	strips × cut × 1.1 + 2 in, rounded up to ⅛ yd	6 × 8 × 1.1 + 2 = 54.8 in = 1⅝ yd
Batting or middle square	finished block − 1 in	6 in

The extra 10% is for shrinkage: flannel shrinks more than quilting cotton, and you should prewash it before cutting so the squares don't shrink unevenly later. The 2 inches straightens the cut edge. With those allowances the calculator gives the same amounts as our flannel rag quilt pattern: 1⅝ yards each for the fronts and backs of the 36 × 43 baby quilt, and 3¼ yards each for the 50 × 64 throw (7 × 9 squares).

The rag edge counts in the finished size. Each seam allowance stays on the front as fringe, including the half inch all around the outside, so the quilt measures one seam allowance more on every side than the blocks alone.

Seam allowance

A rag quilt's seam allowance is the fringe, so it's much wider than the usual quarter inch. Half an inch is the most common choice and what our pattern uses. Five-eighths gives a fluffier rag and costs a little size: each 8-inch square finishes at 6¾ instead of 7. Three-quarters is bushier again, and suits big blocks where the lost size matters less. A narrow allowance leaves little to fray, so the seams look thin.

Keep the seam allowance the same on every seam, including the line around the outer edge, or the rag will look uneven.

Layers

Batting in the middle (the pattern's choice): warm and puffy, with an X of stitching through each block to hold it. Cotton batting is usual.
A third flannel square instead of batting: softer and heavier, and it washes well. The calculator adds the middle squares to the yardage.
Two layers only, for a lighter quilt for summer or for a baby. It's also the quickest to make.

Any layer that sits inside the block is cut 1 inch smaller than the finished block, so there's half an inch of clear space inside each seam line. The calculator always works it out that way.

Using a packaged batt for the squares? The calculator reports the smallest standard size that yields enough. Thirty 6-inch squares come out of a crib batt (45 × 60 inches gives 7 × 10 = 70), and so do the throw's 63.

Common mistakes

Mistake	Result	Fix
Cutting before prewashing	Squares shrink by different amounts; rows don't line up	Prewash and dry every flannel first, then cut
Batting as big as the squares	Seams are stiff and won't fray	Cut batting 1 in smaller than the finished block
Sewing right sides together	The fringe ends up on the back	Put blocks back to back, so allowances face the front
Clipping through the stitching	A hole that keeps growing in the wash	Snip to about ⅛ in from the seam; spring-loaded snips help
Quilting cotton for the fronts	Thin, flat rag	Use flannel, homespun or denim on the side that frays

The flannel rag quilt pattern has the sewing steps, with clipping and washing. Rag quilts are a good use for old flannel shirts in a memory quilt. If you plan to donate one, check the rules first: Quilts for Kids doesn't accept rag quilts, as the charity quilt size guide notes. After the first wash, how to wash a quilt covers lint and drying.

Rag quilt calculator