Seam Allowance Calculator for Cut Size

Add the seam allowance to both opposing edges of each dimension. A piece grows by twice the allowance in width and twice in height, so a 1/2 inch allowance adds 1 inch to the finished width and 1 inch to the finished height.

Garment sewing usually uses 5/8 inch, quilting uses 1/4 inch, and many home decor and bag projects use 1/2 inch. Use whatever your pattern specifies so the finished size comes out right, and the preset buttons cover the four most common values.

Cut to the cut size, then sew on the seam line to reach the finished size. Finished size is the piece after sewing, and cut size includes the allowance the machine will consume in the seams.

Yes. The allowance is added to every edge, so each dimension is increased by two allowances. Enter a zero allowance to cut exactly on the finished line, for example when a pattern already includes the seams.

This calculator applies one allowance to every edge, which suits the vast majority of straight seams. If a specific edge needs a wider allowance, run the tool once for that dimension with its own allowance value.

Those need extra beyond the seam allowance. Add hem depth and facing width separately to the relevant edges, since a folded hem is usually much wider than a normal seam allowance.

Yes. Type the decimal value, such as 0.375 for 3/8 inch or 0.625 for 5/8 inch, or tap a preset. The allowance field steps in eighths of an inch to match common sewing increments.

The fields are labeled in inches, so enter inch values for a direct answer. To work in centimeters, convert your finished sizes and allowance to inches first, since the math of adding twice the allowance is identical in any unit.

Yes. The calculation runs locally in your browser and nothing is uploaded, so your measurements never leave your device.