🧵 Button Size Calculator
A sewing button size calculator that converts between ligne (L), millimeters, and inches, with typical garment use by size.
Typical use at this size: Shirt front / sport shirt
What Button Size Calculator Does
Button sizing has used the same unit — ligne — since long before the metric system existed, and the conversion factor looks arbitrary only because it comes from cross-referencing two unrelated measurement systems: ligne was fixed so that exactly 40 ligne equals 1 inch, which is where the 0.635mm-per-ligne figure comes from (25.4mm ÷ 40).
Because ligne never got replaced the way most old units did, a lot of confusion in practice is not the arithmetic — it is not knowing which system a pattern or supplier is even using, since the same button can be labeled 18L, 11mm, or 0.43" depending on the source.
How to Use Button Size Calculator
- Enter the button size and select which unit you have (ligne, mm, or inches)
- Read the converted values in the other two units
- Check the typical-use suggestion for that size range
Formula Used by Button Size Calculator
Ligne, millimeter, and inch conversion
1 ligne = 0.635 mm = 1⁄40 inch
Worked example
An 18L button (a common shirt-front size)
- mm: 18 × 0.635 = 11.43 mm
- inches: 11.43 ÷ 25.4 = 0.450"
Result: 18L = 11.4 mm = 0.45 inches
Typical button use by ligne size
General guidance — always check the specific pattern or garment's own requirement.
| Ligne range | Typical use |
|---|---|
| 13–16L | Shirt collar / cuff |
| 17–20L | Shirt front / sport shirt |
| 21–24L | Sleeve / pant waistband |
| 25–30L | Blouse / dress |
| 31–36L | Suit jacket |
| 37–45L+ | Coat / overcoat |
Source: WAWAK — Button Size Chart
How to Read Your Result
Ligne is unusual among old units for never being replaced
Most pre-metric trade units (points for type, denier for thread) either converted to metric equivalents or fell out of use entirely. Buttons are a rare case where an inch-derived unit from centuries ago remains the primary sizing reference across the global industry, metric-using countries included, simply because every existing tool, pattern, and supplier catalog is already built around it.
Pattern instructions often specify a range, not one exact size
A sewing pattern calling for "18L-20L buttons" is giving a workable range rather than one precise size, because button placement and buttonhole size usually have some tolerance — this tool's exact conversions are still useful for checking a specific button is within that range.
Limitations & Accuracy Notes
- Typical-use ranges are general sewing-industry guidance, not a rule — many garments deliberately use non-standard button sizes for design reasons.
- Non-circular buttons are measured at their longest point, which this tool does not distinguish from a circular diameter.
Frequently Asked Questions
What is a ligne?
Why is 1 ligne such an odd number in millimeters (0.635)?
What size button do I need for a shirt vs a coat?
Is this the same everywhere in the world?
How do I measure a button I already have?
What does the "L" printed on a button card mean?
Is my data stored?
References & Further Reading
- WAWAK — Button Size Chart — Source of the 1 ligne = 0.635mm conversion (derived from 40L = 1 inch) and the typical-use-by-size guidance used above