Button sizes are quoted in ligne (written “L”), a unit inherited from 18th-century French button makers and still the global standard on tech packs. The conversion is simple: 1 ligne = 0.635 mm, so a 20L button is 12.5 mm across.
Ligne to millimeter conversion chart
| Ligne | Millimeters | Inches | Typical use |
|---|---|---|---|
| 12L | 7.5 mm | 0.30" | Baby clothes, doll clothes, shirt collars |
| 14L | 9 mm | 0.35" | Shirt collars & sleeve plackets |
| 16L | 10 mm | 0.40" | Shirt fronts (slim), blouses |
| 18L | 11.5 mm | 0.45" | Dress shirt fronts — the classic size |
| 20L | 12.5 mm | 0.50" | Polo shirts, casual shirts |
| 24L | 15 mm | 0.60" | Trousers, shirt-jackets, sleeve buttons on suits |
| 28L | 18 mm | 0.70" | Cardigans, light jackets |
| 32L | 20 mm | 0.80" | Suit jacket fronts, blazers |
| 36L | 23 mm | 0.90" | Heavy blazers, light coats |
| 40L | 25 mm | 1.00" | Coats, jackets |
| 44L | 28 mm | 1.10" | Overcoats, duffle coats |
| 54L | 34 mm | 1.35" | Statement coats, capes, decorative |
Three rules of thumb when choosing size
1. Match the buttonhole, not the other way round
A buttonhole should be the button diameter plus 2–3 mm (plus thickness for domed or shank buttons). If the garment is already patterned, measure the buttonhole and work backwards.
2. Heavier fabric, bigger button
Fabric weight and button size scale together: 18L on poplin shirting, 32L on a wool blazer, 44L on a Melton overcoat. An undersized button on heavy fabric slips; an oversized one distorts light fabric.
3. Keep thickness in mind for machine sewing
Automatic button-sew machines have thickness limits (commonly 2–4 mm for flat 4-hole buttons). If your factory sews by machine, confirm button thickness as well as diameter — we list both on every quotation.
Jeans buttons and snaps use millimeters, not ligne
Denim tack buttons are sold by mm: 17 mm for most fashion jeans, 20 mm for heavyweight, 22–25 mm for workwear. Snap fasteners are likewise quoted by cap diameter (9.5–20 mm). When in doubt, mail us a sample garment and we'll measure and match it.
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