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Seam Allowance Calculator

Enter the finished width, height and seam allowance per side to get the cut dimensions.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

Seam allowance is the extra fabric left beyond a garment's finished seam line so pieces can be sewn together without ending up too small. This calculator applies cut size = finished size + (2 × seam allowance) to each dimension, since allowance is added on both opposing edges of a piece.

Standard allowances vary by project — commonly 1.5 cm (5/8") for garment sewing and 0.6–1 cm for quilting — and using the wrong one is a frequent source of pieces that don't align. Sewists and pattern drafters use this math to cut fabric to the correct size the first time and avoid running short mid-project.

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