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?

Ease is the gap between your BODY measurement and the finished garment. Enter your body bust/waist/hip, then add ease: for woven fabrics close-fitting 2-3 cm, standard fit 5-8 cm, loose fit 10-15 cm (measured around the full girth). For knits with good stretch, ease can be zero or negative (compression garments) — the calculator adds ease, then applies the stretch factor.

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. Set the stretch factor below 1.0 in Advanced Options to cut pieces smaller than the body measurement — a 0.85 factor gives roughly 15% negative ease, so a stretchy garment hugs the body rather than hanging loose.

How much thread do I need?

A 301 lockstitch uses about 5.7 times the seam length in total — roughly 3 times the seam length from the needle plus 2.7 times from the bobbin (American & Efird figures) — so allow around 6 times once waste is included. A typical blouse uses 100-150 metres, a dress 150-250 metres. A 4-thread overlocker uses far more (10-15× per seam), so buy several cones.

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

Your body bust measurement (ease is added below)

Waist

Your body waist measurement

Hip

Your body hip measurement

Garment Length

Finished length from shoulder/waist to hem

Seam AllowanceUK commercial patterns use 1.5 cm; indie/knit often 1 cm

Number of Seams

Count of seams to stitch (for thread estimate)

Hem Allowance

Turn-up at the hem: 3 cm standard, 5 cm deep, 1–2 cm narrow

How We Calculate This

Cut Dimension Calculation

Finished Girth = (Body Measurement + Ease) × Stretch Factor

Cut Width (per main piece) = Finished Girth ÷ 2 + (Seam Allowance × 2)

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

Enter your body measurements; ease is the extra room added for comfort and style (woven garments need 5-8 cm at the bust for a standard fit). The front and back are each half the finished girth plus a seam allowance on both side seams. For stretch knits, a stretch factor below 1.0 multiplies the girth down to give negative ease.

Total fabric assumes 150 cm goods folded selvedge-to-selvedge with the main pieces cut on the fold, plus about 15% for sleeves, facings and cutting-layout waste. One-way (nap) fabrics and large pattern repeats need more — add roughly one extra repeat per major piece.

Frequently Asked Questions

Related Calculators

Seam Allowance Fabric Calculator

Calculate total fabric needed for multiple pattern pieces with seam allowances added to every edge, including waste percentage and cutting layout.

Dart Calculator

Calculate dart dimensions for shaping bodices, skirts and trousers.

Pleat Calculator

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

Gather Calculator

Calculate fabric width needed for gathered sections based on fullness ratio.

Ruffle Calculator

Work out fabric requirements for ruffles and flounces.

Last updated: February 2026

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