How it works
Binding length = 2 × (width + length) + extra
Strips = round up( binding length ÷ usable width )
Fabric = strips × strip width ÷ 36, rounded up to ⅛ yd
Binding goes around the whole perimeter. The extra allowance (10" by default) covers the diagonal seams between strips, the folds at the four mitered corners and the overlap where the two ends meet. Strips are cut across the width of fabric (WOF), from selvage to selvage.
Fat quarter option: a fat quarter is about 18" × 21". Strips are cut parallel to the 21" side, so each strip is 21" long, and 18" ÷ strip width tells you how many fit. With 2½" strips that is 7 per fat quarter.
Worked example
A 60" × 80" quilt has a 280" perimeter. Add 10" and you need 290" of binding. At 42" per strip that is 6.9 strips, so cut 7. Seven 2½" strips use 17½" of fabric, so buy ½ yard.
Common mistakes
- Buying the exact inches. Cutters need a straight edge first, so round up to the next ⅛ yard. The calculator already does this.
- Forgetting the joins. Each diagonal join uses a few inches of strip.
- Mixing up finished binding width and strip width. A 2½" strip folded double makes about a ⅜" binding.
Measure the quilt after the borders are on. The border calculator gives the new size of the top, and the fat quarter calculator shows what else you can cut from a scrappy stash.
Last checked October 2026 against standard quilting and knitting math. Found a mistake? Tell us and we’ll fix it.