Standard Seam Allowances by Type
Different sewing techniques require different seam allowances. Using the wrong allowance means your pieces won't fit together properly — too little and you can't finish the seam, too much and you waste fabric and add bulk.
| Seam Type | Allowance | Best For | Notes |
|---|---|---|---|
| Standard | 5/8" (1.6 cm) | Most garments | US pattern industry standard |
| French seam | 5/8" (1.6 cm) | Sheer/lightweight fabrics | Enclosed raw edges, sewn twice |
| Flat-felled | 5/8" (1.6 cm) | Jeans, shirts, sportswear | Strong, visible topstitch |
| Overlock/serger | 3/8" (1 cm) | Knits, activewear | Trimmed during stitching |
| Quilting | 1/4" (0.6 cm) | Quilt piecing | Scant 1/4" for accuracy |
| European patterns | 3/8" (1 cm) | Burda, European brands | Narrower than US standard |
Hem Allowances by Type
| Hem Type | Allowance | Use For |
|---|---|---|
| Narrow rolled hem | 1/4-3/8" | Silk, chiffon, lightweight fabrics |
| Single fold hem | 1" | Knit tops, casual garments |
| Double fold hem | 1.5-2" | Skirts, dresses, pants |
| Blind hem | 2-3" | Dress pants, formal garments |
| Shirt tail hem | 1/4-3/8" | Curved shirt hems |
FAQ
Do I add seam allowance to commercial patterns?
Most US commercial patterns (Simplicity, McCall's, Butterick, Vogue) already include 5/8-inch seam allowance. European patterns (Burda) often do NOT include seam allowance — you must add it yourself. Always check the pattern instructions.
How do I convert between metric and imperial seam allowances?
The standard 5/8 inch = 1.6 cm. Most metric patterns round to 1.5 cm. The 1mm difference is negligible. For quilting, 1/4 inch = 6.35mm — metric quilters use 6mm or 7.5mm depending on their ruler markings.
Should I add extra for cutting inaccuracy?
No. Cut on the line. If your cutting is consistently inaccurate, the fix is a better technique (rotary cutter + ruler), not wider seam allowances. Adding "safety margin" creates fit problems because the extra fabric has to go somewhere.
Related Tools
- Fabric Yardage Calculator — how much fabric for your project
- Bias Tape Calculator — fabric for bias binding
- Quilt Size Calculator — dimensions and fabric for any quilt