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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
Trousers: 3–4cm. Straight skirts: 4–5cm. A-line skirts: 2–3cm. Circle skirts: 0.5–1cm (narrow rolled). Shirts: 1–2cm. The more curved the hem, the narrower it should be.
A double-turned (or double-fold) hem folds the raw edge under once, then folds again by the hem depth. It encloses the raw edge completely. The total allowance needed is twice the finished hem depth.
Blind hems are ideal for tailored garments where you do not want visible stitching on the outside. The stitches catch only a tiny amount of the outer fabric, making them nearly invisible. They work best on medium to heavy fabrics.
Hem tape (or hem webbing) is fusible tape placed between the hem fold layers. When pressed with an iron, it bonds the layers together without stitching. Buy tape slightly longer than the garment circumference.
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Last updated: February 2026
All calculations are estimates. Always verify quantities before cutting or purchasing fabric.