Hem Calculator — Hem Allowances & Types
Calculate the hem allowance to add per edge for different hem types, plus the length of hem tape to buy.
How We Calculate This
The hem allowance is the extra fabric you add below the finished hemline before cutting. It depends on the hem type:
- Single turn: Hem depth + 0.5cm turn-under (raw edge folds under once by ~0.5cm, typical dressmaking practice)
- Double turn: Hem depth × 2 — a double-fold hem turns up the full depth twice, so you need twice the finished depth (TREASURIE, Guthrie & Ghani)
- Narrow rolled: 1.5cm total, fixed — stitch ~1cm from the raw edge, then roll (Maven Patterns). The Hem Depth field is ignored for this type.
- Blind hem: Hem depth + 1cm fold-back, so the raw edge can be folded back on itself for the catch stitch (typical practice)
- Faced hem: 1.5cm, fixed — the edge turns up by only a seam allowance because a separate facing piece finishes it. The Hem Depth field is ignored for this type.
Hem tape/web length is the hem edge (your garment circumference) plus a small ease margin for the join.
Frequently Asked Questions
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Last updated: February 2026
All calculations are estimates. Always verify quantities before cutting or purchasing fabric.