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Quilt Block Calculator — Blocks & Fabric
Calculate the number of blocks and fabric needed for your quilt layout.
How We Calculate This
The calculator determines how many blocks fit across and down the quilt, then calculates fabric needed to cut all blocks from a single fabric.
The formula
Blocks across = ceil(Quilt width ÷ Block size)
Blocks down = ceil(Quilt length ÷ Block size)
Cut size = Block size + (Seam allowance × 2)
Fabric rows = ceil(Total blocks ÷ Blocks per fabric row)
Frequently Asked Questions
Common quilt block sizes are 15cm (6in), 20cm (8in), 25cm (10in) and 30cm (12in) finished. The most popular size is 30cm (12in) finished. Smaller blocks create more visual interest; larger blocks are faster to sew.
The standard quilting seam allowance is a quarter inch, which is 6mm (0.6cm) in metric — exactly 0.635cm. Many metric quilters round to 6mm or use 0.5cm. Do not use 0.75cm: that is 7.5mm (just under 5/16in), not a quarter inch, and it will make every block slightly oversized. Some patterns specify 1cm. Always use a consistent seam allowance throughout.
Add two seam allowances to the finished block size. For a 15cm finished block with a 0.6cm (quarter inch) seam allowance: 15 + (0.6 x 2) = 16.2cm cut size.
It is wise to make 1-2 extra blocks in case of errors or design changes. Extra blocks can be used for pillow covers, labels, or practice quilting.
Related Calculators
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Calculate binding strip fabric and length for finishing quilts.
Strip Piecing Calculator
Calculate strip quantities for strip-pieced quilt blocks and designs.
Sashing Calculator
Calculate sashing strip quantities and fabric for quilt layouts.
Border Calculator
Calculate fabric needed for single or multiple quilt borders.
Quilt Label Calculator
Calculate label dimensions and fabric needed for quilt care labels.
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Last updated: February 2026
All calculations are estimates. Always verify quantities before cutting or purchasing fabric.