Quilt Calculator (blocks, finished size, backing & binding yardage)

Understanding the quilt size calculator — concept and principle

This calculator plans a block quilt: how many blocks across and down for a target size, the finished size with sashing and borders, the backing and batting size, how much backing fabric to buy and the binding needed. Quilters use it to plan a bed or lap quilt before cutting.

Blocks to finished quilt: with the default inputs the result is 68 × 80 in backing (2 widths, 3.78 yd).

How it is calculated

Blocks across = round((target width − 2 × border + sashing) ÷ (block + sashing)); likewise down.
Finished size = blocks × block + (blocks − 1) × sashing + 2 × border.
Backing and batting = finished size + 2 × extra on each side.
Backing is pieced from whole fabric widths: the calculator tries seams running down and across and keeps the layout needing less fabric (yards = widths × panel length ÷ 36).
Binding = perimeter + 12 in; strips of 2½ in joined on the diagonal.

The principle

A quilt top is a grid of blocks separated by optional sashing strips and framed by borders. Working out how many whole blocks fit, then rebuilding the size from them, gives the real finished size, which may differ slightly from your target. Backing and batting must be larger than the top because quilting draws the layers in and the edges need trimming. Standard fabric is narrower than most quilts, so the backing is made from two or more widths sewn together; turning the seams the other way can save fabric.

Worked example

Default inputs: target 60 × 72 in, 12 in blocks, no sashing, 6 in borders, fabric 42 in, 4 in extra.

Across = round((60 − 12) ÷ 12) = 4; down = round((72 − 12) ÷ 12) = 5; 20 blocks.
Finished = 4 × 12 + 12 = 60 by 5 × 12 + 12 = 72: 60 × 72 in.
Backing and batting = 68 × 80 in.
Seams down: 2 widths × 80 in = 160 in; seams across: 2 widths × 68 in = 136 in → 2 widths, 3.78 yd.
Binding = 264 + 12 = 276 in, 7 strips.

Each point is the calculator re-run with only “Finished block size (in)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Finished block size (in)	Blocks needed
3	320
6	80
9	35
12	20
15	12
18	9
24	6

How to read the result

Block fabric depends on the block pattern and is not included. Buy a little extra backing for straightening and shrinkage. If the finished size is not quite what you want, try a different border width or block count.

Common mistakes

Forgetting seam allowances when cutting blocks; the block size here is finished.
Making the backing the same size as the top.
Using full fabric width including selvages.
Forgetting that wide-back fabric can avoid seams altogether.

Keep in mind: Fabric widths and shrinkage vary. Measure and pre-wash as your pattern advises.

Frequently asked questions

How many 12 in blocks for a 60 × 72 quilt?

20 blocks (4 × 5) with 6 in borders.

How big should the backing be?

About 4 in larger than the top on every side: 68 × 80 in here.

How much backing fabric do I need?

About 3.8 yards of 42 in fabric for this quilt.

Sources: Layout geometry of block quilts (blocks, sashing, borders and backing pieced from fabric widths), as used in standard quilting references

Checked 9 Nov 2026. Layout geometry of a block quilt (blocks, sashing and borders), piecing the backing from whole fabric widths and joining binding strips; fabric width, backing extra and the 2½ in binding strip are example values. 1 yd = 36 in.

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