Quilt Calculator
Calculate how many blocks, how much fabric and how much binding a quilt needs.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Quilt maths is mostly about seam allowances, because every block loses half an inch in both directions once it is sewn. Planning from the finished quilt size backwards through the block size is what keeps the borders even.
Worked example
calculated with the default values below
Finished quilt width 60 in · Finished quilt length 80 in · Finished block size 10 in · Seam allowance 0.25 in · Fabric width 44 in · Binding strip width 2.5 in Blocks across 6 · Blocks down 8 · Total blocks 48 · Cut block size (with seam allowance) 10.50 in · Fabric for the top 3.79 yards · Fabric for binding 0.49 yards · Fabric for backing 3.33 yards
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
n = ⌈W÷s⌉×⌈L÷s⌉; Y = W×L÷(F×36)×1.25; Yb = ⌈2(W+L)÷F⌉×Bw÷36
- W
- Quilt width (in)
- L
- Quilt length (in)
- s
- Finished block size (in)
- F
- Fabric width (in)
- n
- Total blocks
- Y
- Top fabric (yd)
- Yb
- Binding fabric (yd)
- Bw
- Binding strip width (in)
Blocks across/down = ceiling(finished dimension / block size); cut size adds twice the seam allowance. Fabric estimates use fixed 25% top and 10% backing allowances; layout, borders, directional prints, shrinkage and cutting plans can change yardage.
Frequently asked questions
Why does each block need an extra half inch for seams?
Every sewn seam hides a seam allowance on both sides, so the cut block is block size plus twice the allowance. At the default 0.25 inch allowance a 10 inch finished block must be cut 10.5 inches, and the 60 by 80 inch quilt needs 6 by 8, or 48 blocks. The top fabric is then quilt area divided by fabric width, with a 25% waste margin.