Definition
Seam allowance
The extra fabric between the stitching line and the raw edge, which is trimmed or pressed inside the finished seam. Commercial sewing patterns almost always use 5/8 inch or 1.5 centimetres, and quilt piecing almost always uses 1/4 inch.
Seam allowance is added to every edge when you cut, and forgetting it on even one edge per piece adds up across four pieces. It is the most common cause of a garment that comes out slightly too small.
Tools that use this term
Seam Allowance Calculator
Add a seam allowance to a finished measurement to get the cut size, and work back from a cut size to the finished size it produces.
Fabric Calculator
Work out how much fabric to buy for a project from its finished size, the seam allowance you are cutting and the width of the bolt you are buying.
Fabric Yardage Calculator
Yardage from finished measurements for a garment, adding seam allowance, hem, layout waste and pattern repeat matching.