🧵 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 still runs on an old unit, the ligne, 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 comes from not knowing which system a pattern or supplier is even using rather than from the arithmetic, 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 rather than 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