Standard Seam Allowances
Seam allowance is the area between the stitching line and the raw edge of the fabric. Getting it right is crucial — too narrow and the seam may fray or pull apart; too wide and you waste fabric or create unnecessary bulk. Different patterns and traditions use different standard seam allowances, which can cause confusion when mixing sources.
Common Seam Allowance Widths
| Width | Metric | When to Use | Notes |
|---|---|---|---|
| ¼″ | 6 mm | Quilting, patchwork | Standard for quilting in both UK and US |
| ⅜″ | 10 mm (1 cm) | Indie / PDF patterns, European patterns | Increasingly common in UK independent patterns |
| ½″ | 12 mm | Craft projects, home decor | Sometimes used on simpler garment patterns |
| ⅝″ | 16 mm | US commercial patterns (Big 4) | Vogue, Butterick, McCall's, Simplicity standard |
| 1 cm | 10 mm | Burda patterns, many European brands | Note: some Burda patterns include NO seam allowance |
| 1.5 cm | 15 mm | UK/European dressmaking, Burda (when included) | Common in UK sewing books and courses |
| 1″ | 25 mm | Fitting adjustments, hems | Extra width for alterations; sometimes used on side seams |
Pattern Convention Differences
| Pattern Source | Seam Allowance Included? | Standard Width | Action Needed |
|---|---|---|---|
| US Big 4 (Vogue, McCall's, etc.) | Yes | ⅝″ (16 mm) | Cut on printed line |
| Burda magazine | No | — | Add 1.5 cm seam allowance when cutting |
| Burda Easy / Burda envelope | Yes (usually) | 1 cm or 1.5 cm | Check instructions — varies by pattern |
| UK indie patterns (PDF) | Yes (usually) | 1 cm or 1.5 cm | Cut on printed line; check instructions |
| Japanese patterns | No | — | Add seam allowance (usually 1 cm) when cutting |
| Drafting from scratch | No (you add it) | Your choice | Add 1–1.5 cm for seams, 2–4 cm for hems |
Always read the pattern instructions first. The seam allowance convention can vary even between patterns from the same company. Getting this wrong is one of the most common sewing mistakes and will affect the fit of the finished garment.
Recommended Allowances by Application
| Application | Recommended Width | Why |
|---|---|---|
| Standard seams | 1–1.5 cm | Enough for a secure seam without excess bulk |
| French seams | 1.5 cm minimum | Needs extra width to enclose raw edges |
| Overlocked / serged seams | 1 cm | The overlocker trims as it sews |
| Necklines and armholes | 6–10 mm | Curves need less width to reduce bulk |
| Hems (skirt / trouser) | 2.5–4 cm | Wider for a stable, weighted hem |
| Hems (shirt / blouse) | 1–2 cm | Narrow double-fold hem |
How to Add or Remove Seam Allowance
- Adding: Trace the pattern piece, then use a ruler or seam gauge to mark the required distance from the cutting line all the way around. A quilting ruler with grid lines makes this quick and accurate.
- Removing / reducing: Measure inward from the cutting line by the amount you need to remove, and redraw. For example, to convert a ⅝″ allowance to 1 cm, trim 6 mm from the cutting line.
- Consistency is key: Whatever width you choose, use the same allowance on all seams of the garment (except hems and facings, which may differ).
- Mark the stitching line on tricky curves and corners using tailor's chalk or a washable marker.
Related Calculators
- Seams & Construction Calculators — seam allowance conversion, fabric requirement adjustments and more
Seam allowance conventions are not standardised across the sewing industry. Always check your pattern instructions before cutting. When in doubt, cut with a larger seam allowance — you can always trim it down, but you can't add fabric back.