What is the standard seam allowance?

In the UK, most commercial patterns include 1.5 cm (5/8 inch) seam allowance. Some independent pattern companies use 1 cm. Japanese patterns often include no seam allowance at all, requiring you to add your own.

How much ease should I add?

For woven fabrics: close-fitting 2-3 cm, standard fit 5-8 cm, loose fit 10-15 cm. For knits with good stretch, ease can be zero or even negative (for compression garments). This calculator adds ease before seam allowance.

Do I need different seam allowance for knits?

Knit fabrics often use 1 cm seam allowance instead of 1.5 cm, as the stretch handles fit adjustments. Use the stretch factor in Advanced Options to reduce cut dimensions for stretch fabrics.

How much thread do I need?

A rough guide is 2.5 times the total seam length for a standard lockstitch. A typical blouse uses 100-150 metres of thread, a dress 150-250 metres. Buy a standard spool (200-500m) and you will have plenty.

Should hem allowance be the same as seam allowance?

No, hems are typically wider: 3 cm for a standard turned hem, 5 cm for a deep hem, 1-2 cm for a narrow rolled hem. This calculator separates hem allowance from seam allowance.

SewCalcs

Seam Allowance Calculator — Total Fabric with Seam Allowances

Calculate cut dimensions and total fabric needed including seam allowances, ease and hems.

Bust

Finished garment bust

Waist

Finished garment waist

Hip

Finished garment hip

Garment Length

Length measurement

Seam Allowance

Seam allowance measurement

Number of Seams

Total seams in garment

Hem Allowance

Enter the hem allowance

How We Calculate This

Cut Dimension Calculation

Cut Width = (Finished Measurement + Ease) / 2 + (Seam Allowance x 2)

Cut Length = Finished Length + Seam Allowance (top) + Hem Allowance (bottom)

Ease is added to the body measurements for comfort. Seam allowance is added to each seam edge. For stretch fabrics, the stretch factor reduces the cut dimensions.

Frequently Asked Questions

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Work out fabric needed for box pleats, knife pleats and inverted pleats.

Gather Calculator

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Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.