Seam Allowance Calculator
Add seam allowance to your pattern pieces. Enter finished dimensions and get cut dimensions with your chosen seam allowance added to each edge.
Seam Allowance Setting
1cm will be added to all sides (total +2.0cm per dimension)
Pieces
Cut Dimensions
| Piece | Finished (cm) | Cut (cm) | +Seam |
|---|---|---|---|
| Front Panel L: 45cm W: 30cm | 45 x 30 | 47.0 x 32.0 | +2.0cm |
| Back Panel L: 45cm W: 30cm | 45 x 30 | 47.0 x 32.0 | +2.0cm |
Tip: Remember to add seam allowance before cutting. Most patchwork projects use 0.5cm or 1cm allowances.
Standard Seam Allowances
Most commercial sewing patterns use 5/8 inch (15 mm) seam allowance for woven fabrics. UK and EU patterns often default to 1.5 cm (15 mm). Knits and stretch fabrics: 1/4 to 3/8 inch (6-10 mm). Quilting: 1/4 inch (6 mm) precisely. Industrial/garment trade: 1 cm (10 mm) common.
When converting between pattern systems, always check the pattern's stated seam allowance - some print 'seam allowance included' (you cut along the line); others 'add seam allowance' (you cut outside the line). Mistaking which can make finished garments 1-2 inches too small. The first piece you cut is the easiest to test and verify before committing the whole pattern.
Seam Allowance by Project Type
| Project | Allowance |
|---|---|
| Quilting | 1/4 in (6 mm) |
| Knit garments | 3/8 in (10 mm) |
| Children's wear | 3/8 in (10 mm) |
| Most adult wear | 5/8 in (15 mm) |
| Tailored/coats | 1 in (25 mm) |
| Curtains/upholstery | 1 in (25 mm) |
| Hems | 1-3 in (25-75 mm) |
Frequently Asked Questions
Why so much variation?
Different fabrics fray and stretch differently. Knit fabrics need less allowance because they don't fray. Quilting needs precise 1/4 inch for piecing accuracy. Heavy fabrics (wool, denim) need more allowance to handle the bulk of bound seams. Match allowance to project.
What if my pattern doesn't say?
Most commercial patterns include the allowance and label it ('5/8 in SA included'). DIY/digital patterns vary - check the pattern's instructions or front cover. When ambiguous, assume 5/8 in / 15 mm and adjust the first muslin/sample if it doesn't fit.
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