Quilt Size Calculator: Blocks, Sashing and Borders

How to calculate quilt size

Add up everything across the quilt: the blocks, the sashing strips between them and the borders on both sides. Do the same down the quilt. Use finished sizes throughout, the size each piece shows once it is sewn in.

Width = blocks across × block width + (blocks across − 1) × sashing + 2 × each border Length = blocks down × block height + (blocks down − 1) × sashing + 2 × each border

Example. Thirty 12 in blocks set 5 across and 6 down with 2 in sashing and a 4 in border: across, 5 × 12 + 4 × 2 + 2 × 4 = 76 in. Down, 6 × 12 + 5 × 2 + 2 × 4 = 90 in. That is a 76 × 90 in quilt, close to a standard twin.

With sashing and cornerstones, every piece is cut 1/2 in bigger than it finishes. Here that is 49 sashing strips 2 1/2 × 12 1/2 in and 20 cornerstones 2 1/2 in square.

Quilt sizes for each mattress

Mattresses come in standard sizes. For a quilt that hangs 12 in down each side and over the foot of the bed, add 24 in to the width and 12 in to the length. Add another 10 in or so to the length if you want to tuck it under the pillows.

Bed	Mattress	Quilt with a 12 in drop
Crib	28 × 52 in	about 36 × 52 in, no drop
Twin	38 × 75 in	62 × 87 in
Twin XL	38 × 80 in	62 × 92 in
Full	54 × 75 in	78 × 87 in
Queen	60 × 80 in	84 × 92 in
King	76 × 80 in	100 × 92 in
California king	72 × 84 in	96 × 96 in

Mattress depths vary from about 8 to 16 in, so measure your own bed when the drop matters.

Planning tips

Adjust with borders. Blocks come in fixed steps. Get close with the number of blocks, then use border width to land on the exact size.
Measure before cutting borders. Measure the finished center through the middle and cut the border strips to that length, not to the theory, so the quilt lies flat.
Plan for shrinkage. Quilting and washing can take an inch or two off a large quilt.

For yardage, enter your pieces in the quilt fabric calculator, then size the back with the quilt backing calculator.

Questions

How do I calculate the size of my quilt?

Multiply the number of blocks across by the finished block width, add the sashing between the blocks and add each border twice. Do the same for the length. Thirty 12 in blocks set 5 by 6 with 2 in sashing and a 4 in border make a 76 × 90 in quilt.

How many 12 inch blocks do I need for a queen size quilt?

For a quilt around 90 × 108 in with no sashing or borders, 9 rows of 12 in blocks make 108 in and 8 across make 96 in, so 72 blocks. With a 6 in border you need fewer: 7 across and 8 down, 56 blocks, also make 96 × 108 in.

How big should a quilt be for a queen bed?

A queen mattress is 60 × 80 in. For a quilt that hangs 12 in over the sides and the foot, make it about 84 × 92 in, and add about 10 in to the length to tuck under the pillows.

What size do I cut sashing and cornerstones?

Cut them 1/2 in bigger than they finish, for the two 1/4 in seam allowances. For 2 in sashing between 12 in blocks, cut strips 2 1/2 × 12 1/2 in and cornerstones 2 1/2 in square.

Should I use finished or unfinished block size?

Use the finished size, the size the block shows once it is sewn into the quilt. A block that measures 12 1/2 in before it is sewn in finishes at 12 in.