Seam Allowance Calculator
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Add seam allowance on all sides to get cutting dimensions from finished piece size.
Finished size + allowance
Cut size
11 × 13 in
Finished 10 × 12 in + 0.5 in allowance per side
- Cut length
- 11 in
- Cut width
- 13 in
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Seam allowance
Seam allowance is the extra fabric beyond the finished stitch line that gets sewn into the seam. Standard garment seams use ⅝ inch (1.5 cm) in US patterns or 1 cm in many European patterns. Quilting often uses ¼ inch.
To find cut size, add twice the seam allowance to each dimension — once per side. A 10 × 12 inch finished rectangle with ½ inch allowance needs a 11 × 13 inch fabric cut.
Example: finished block 9 inches square with ¼ inch seam allowance → cut 9.5 × 9.5 inches. For 1 cm allowance on a 20 × 30 cm finished piece, cut 22 × 32 cm.
Common questions
Is seam allowance added on every side?
Yes for enclosed pieces. Hems and facings may use different allowances — check your pattern instructions for each edge.
What allowance do most patterns use?
US commercial patterns often include ⅝ inch (1.5 cm). Indie PDF patterns frequently specify ⅜ or ½ inch. Quilting patterns commonly use ¼ inch.