Quilt Block Size Calculator

Start from the finished quilt size you want, and work backward to the block size that gets you there.

Finished quilt width (in)

Finished quilt length (in)

Blocks across

Blocks down

Sashing width between blocks (in, 0 if none)

Border width, each side (in, 0 if none)

Seam allowance, each side (in)

How the math works

Start with the finished quilt dimension, subtract the border on both sides and the sashing between blocks, then divide what's left by the number of blocks in that direction — that gives the finished size of one block. Add seam allowance on all four sides to get the size to actually cut the block at.

Blocks don't have to be square

If your width and length math give different block dimensions, that's normal for a rectangular quilt with a fixed block count in each direction — it just means your blocks are rectangles rather than squares. If you want square blocks, adjust the number of blocks across or down until both calculations land on the same number.

Sashing and borders are optional inputs, not required

Leave sashing and border width at 0 if your quilt design doesn't use them — some quilts are simply blocks sewn directly edge to edge with no border at all.