CraftNumaV0.1

Sewing & fabric

Rectangular seam allowance

Find the cutting dimensions of a rectangle from its finished dimensions and an equal allowance on every edge.

Use a single decimal point or comma, without thousands separators or unit symbols. All lengths use the selected unit. Values must be 0–1,000,000; dimensions and swatch counts must exceed zero. Counts must be whole numbers. Extra allowance: 0–100%; lengthwise shrinkage: 0–50%.

Your results

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Assumptions & limits

The same allowance is added to all four edges. Use seam-line dimensions without an existing allowance. This is not a curved-pattern offset tool; hems, turn of cloth and construction details may need different allowances.

Formula

cutWidth = w + 2s; cutLength = l + 2s; area = cutWidth × cutLength

w
Finished piece width
l
Finished piece length
s
Allowance on each edge

Worked example

10 in × 20 in; s = 0.5 in → 11 in × 21 in; 231 in².

Results show up to 8 decimal places. Small values use scientific notation; calculations use unrounded factors.

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