# Seam allowance chart

Seam allowances cluster around seven values: a quarter inch for patchwork, three-eighths for overlocked knits, 1 cm for European patterns and bag making, half an inch for general home sewing, 1.5 cm as the metric dressmaking standard, five-eighths of an inch as the imperial one, and 2 cm for curtains and loose covers. Five-eighths is 15.875 mm rather than 15 mm, so sewing a metric 1.5 cm on an imperial pattern finishes wider on every seam.

Source: https://fabricmeasure.com/charts/seam-allowance-chart/
Last updated: 2026-08-20 (method v1)
Published by FabricMeasure.

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## The table

Listed smallest first: the labels do not sort the way people assume. 1 cm falls
between 3/8 in and 1/2 in, and 1.5 cm is SMALLER than 5/8 in rather than equal to it.

| Allowance | Millimetres | Inches | Centimetres | Where it is used |
| --- | --- | --- | --- | --- |
| ¼ in | 6.35 mm | ¼ in | 0.64 cm | Patchwork and quilting, where every seam is pieced. |
| ⅜ in | 9.52 mm | ⅜ in | 0.95 cm | Overlocked knits and fine seams. |
| 1 cm | 10 mm | ⅜ in | 1 cm | European patterns, bag making, home furnishing. |
| ½ in | 12.7 mm | ½ in | 1.27 cm | General home sewing, US patterns for straight seams. |
| 1.5 cm | 15 mm | 9/16 in | 1.5 cm | The metric dressmaking standard. |
| ⅝ in | 15.88 mm | ⅝ in | 1.59 cm | The imperial dressmaking standard. Not the same as 1.5 cm. |
| 2 cm | 20 mm | 13/16 in | 2 cm | Curtains, loose covers, anything that may be let out. |

### The substitution that matters

5/8 in is 15.875 mm. 1.5 cm is 15 mm. The gap is 0.875 mm per seamed edge, and it
always runs the same way: sewing metric on an imperial pattern finishes WIDER.
Across eight seamed edges that is 7 mm, which is most of a size grade.

### Which edges take an allowance

- A seamed edge takes one allowance (this piece only; the piece it joins carries its own).
- A hemmed edge takes the whole hem — twice its depth if turned twice.
- A folded edge takes nothing.
- A selvedge used as a finished edge takes nothing.

Always work from the finished size outwards. Working back from a cut size requires
knowing what was already added, which is what a pattern tends not to print.

## Common questions

### Is a 5/8 inch seam allowance the same as 1.5 cm?

Not quite. Five-eighths of an inch is 15.875 mm and 1.5 cm is 15 mm, a difference of 0.875 mm per seam. On one seam it is invisible. On a bodice with eight seamed edges it is 7 mm of finished width, which is most of a size grade.

### Why is patchwork sewn at a quarter inch?

Because a quilt block has dozens of seams meeting at its corners, and a wide allowance would create a lump where they cross. A quarter inch is 6.35 mm — enough to hold, small enough that six of them can meet without the block distorting. Many quilters sew a scant quarter inch, a thread narrower still, to allow for the fabric that turns the fold.

### Does every edge take an allowance?

No, and treating all four edges the same is the usual mistake. A seamed edge takes one allowance. A hemmed edge takes the whole hem, twice its depth if it is turned twice. A folded edge, where the piece is cut on a fold and opens out, takes nothing at all, and neither does an edge left on the selvedge and used as a finished edge.

### Why do curtains use 2 cm when dressmaking uses 1.5?

Because curtains may need letting out. A generous allowance leaves cloth to work with if a hem has to drop or a width has to be re-seamed, and the extra bulk does not matter in a heavy furnishing fabric hanging in folds. The same reasoning applies to loose covers.

## Related tools

- [Seam allowance calculator](https://fabricmeasure.com/calculators/seam-allowance-calculator/): Finished size to cut size — and what a different allowance does to the garment you end up with.
- [Cushion fabric calculator](https://fabricmeasure.com/calculators/cushion-fabric-calculator/): Cover size, back opening and piping in; the length to buy and a row-by-row cutting plan out.
- [Fabric yardage calculator](https://fabricmeasure.com/calculators/fabric-yardage-calculator/): Piece size, how many, roll width — the length to buy, and the strip you pay for but never cut.
- [Fabric width chart](https://fabricmeasure.com/charts/fabric-width-chart/): Standard roll widths in both systems, and the gap between the label and the cloth.