Hong Life CalculatorsUnderstanding the quilt binding calculator — concept and principle
This calculator works out how many strips to cut for straight-grain quilt binding, how long the joined strip will be and how much fabric to buy. Quilters use it to finish a quilt edge without running short.
How it is calculated
- Binding length = quilt perimeter 2 × (width + length) + extra for corners and the end join.
- Each strip is cut across the fabric, so it is as long as the usable width F.
- Each join loses length: a diagonal seam loses one strip width w; a straight seam loses ½ in.
- Strips n = ⌈(length − loss) ÷ (F − loss)⌉; joined length = n × F − (n − 1) × loss.
- Fabric = n × strip width (1 yd = 36 in; 1 in = 2.54 cm).
The principle
Binding wraps the raw edges of the quilt, so it must go all the way round plus a little for mitred corners and the final join. Cutting strips across the fabric gives the longest pieces from a small amount of fabric. Joining strips with a 45° diagonal seam spreads the bulk of the seam allowance so it does not make a lump, but the overlapping square uses up one strip width of length at each join. The strip count is the smallest whole number whose joined length covers what you need.
Worked example
Default inputs: quilt 60 × 72 in, strips 2.5 in wide, usable fabric 42 in, extra 12 in, diagonal joins.
- Perimeter = 2 × (60 + 72) = 264 in; binding needed = 264 + 12 = 276 in.
- Strips = ⌈(276 − 2.5) ÷ (42 − 2.5)⌉ = ⌈6.92⌉ = 7, with 6 seams.
- Joined length = 7 × 42 − 6 × 2.5 = 279 in.
- Fabric = 7 × 2.5 = 17.5 in = 0.49 yd = 44 cm.
| Usable fabric width (in) | Strips to cut (across the fabric width) |
|---|---|
| 10.5 | 35 |
| 21 | 15 |
| 31.5 | 10 |
| 42 | 7 |
| 52.5 | 6 |
| 63 | 5 |
| 84 | 4 |
How to read the result
Buy a little more than the calculated fabric to straighten the cut edge and allow for shrinkage. A 2½ in strip folded in half gives a common double-fold binding; narrower strips give a slimmer finished edge. Curved or scalloped edges need bias binding, which is cut and calculated differently.
Common mistakes
- Forgetting the extra for corners and the closing join.
- Using the full fabric width including selvages.
- Joining with straight seams but calculating with diagonal-seam loss, or the reverse.
- Using straight-grain binding on curved edges.
Frequently asked questions
How much binding do I need for a 60 × 72 quilt?
About 276 in, including 12 in extra: seven 2½ in strips from 42 in wide fabric.
How much fabric is that?
About ½ yard (17.5 in).
Why join binding strips on the diagonal?
It spreads the seam bulk so the binding lies flat.
Sources: Geometry of strip piecing (perimeter, strip count and length lost per join), as used in standard quilting references