Quilt Size Calculator
Plan the quilt before you cut a single block. Set your block size and layout, add sashing and borders, and see the finished dimensions — then check it against a bed with your preferred drop and pillow tuck.
Use finished sizes, not cut sizes. Sashing sits between blocks; borders wrap the outside.
Formula & how it works
Width is columns × block + sashing × (columns − 1) + border × 2, and length uses rows the same way. Sashing appears only between blocks, not around the outside.
Bed requirement is mattress width + drop × 2 by mattress length + drop + pillow tuck. Backing adds 4 inches of overhang per side.
Worked example
Thirty 12-inch blocks set 5 across by 6 down, with 2-inch sashing and a 4-inch border, finish at 76 × 90 inches. On a queen mattress wanting a 10-inch drop you need at least 80 × 90 — so this quilt is a little narrow, and widening the border to 6 inches would fix it.
Planning quilt dimensions
Sashing counts between, borders count twice
The most common arithmetic slip is adding sashing around the outside as well as between blocks. Five blocks across have only four sashing strips between them, while the border adds its width to both edges — so it contributes double.
Design to the bed, not the chart
Published quilt sizes assume a standard mattress, but pillow-top and deep mattresses have grown considerably. Measuring your actual bed and deciding how far you want the quilt to hang gives a target that will genuinely fit, rather than one that stops short of the mattress edge.
Adjust with the border
When a block layout lands close to but not quite at your target, the border is the easiest dial to turn — it changes both dimensions without altering the block count or piecing. Adding an inch to the border adds two to the finished width and length.