Quilt size & block calculator
Enter the size you want the quilt to be, the finished block size and any sashing and border. You get the number of blocks across and down, the real finished size, the cut size of each block with seam allowances, and the backing and binding to buy.
Size you want
Blocks and borders
About the quilt size & block calculator
Enter the size you want the quilt to be, the finished block size and any sashing and border. You get the number of blocks across and down, the real finished size, the cut size of each block with seam allowances, and the backing and binding to buy.
Part of SmartCalcy’s crafts & sewing tools. It runs in your browser with no account, uses your own currency and units (change them at the top of the page), and gives estimates for information only, so check official guidance before you rely on a result.
How to use the quilt size & block calculator
What it calculates and when to use it
Plans a quilt made of square blocks: blocks across and down for the size you want, the real finished size, the cut size of each block, and the backing and binding to buy.
How to use it, step by step
- Enter the quilt size you want.
- Enter the finished block size, and any sashing and border width.
- Enter your seam allowance.
- Read the blocks needed and the sizes to cut.
What each input means
- Quilt width and length – Starts at 150 × 200 cm.
- Finished block size – Starts at 25 cm.
- Sashing – Strips between blocks; 0 for none.
- Border – Starts at 10 cm.
- Seam allowance – 0.75 cm or ¼ in.
How to read the results
- Blocks needed – Across × down, with the finished quilt size.
- Sizes – Cut block size, quilt centre, sashing strips, backing and binding.
The formula
Blocks across = round((width − 2 × border + sashing) ÷ (block + sashing)). Cut block = finished block + 2 × seam allowance.
A worked example
With the starting entries: (150 − 20) ÷ 25 = 5.2, so 5 across; (200 − 20) ÷ 25 = 7.2, so 7 down: 35 blocks, cut at 26.5 cm, for a finished quilt of 145 × 195 cm.
Assumptions and limits
- Blocks are square and the same size.
- Backing is 10 cm (4 in) larger on every side for quilting.
Common mistakes
- Cutting blocks at the finished size without seam allowances.
- Not checking block sizes before joining rows.
Frequently asked questions
What seam allowance do quilters use?
Usually ¼ in (about 0.75 cm).
Why is the finished size different from what I entered?
Only whole blocks fit; adjust the border to get closer.
Related tools
Sizes
- Cut each block
- 26.5 × 26.5 cmfinished 25 + 2 × 0.75 seam
- Quilt centre
- 125 × 175 cm
- With borders
- 145 × 195 cm
- Backing
- 165 × 215 cm10 cm larger on every side for quilting
- Binding
- 710 cmperimeter plus extra for corners and joining