The Button Size Decoder: Ligne, Millimetres and Shopping Without Guesswork
Photo: Joe Haupt from USA, CC BY-SA 2.0, via Wikimedia Commons
Button sizing has a reputation for being unnecessarily mysterious. You find a pattern that asks for 15mm buttons, a vintage card labelled 24L, and an online listing that says 'large' as if that settles it. Before you know it, you're staring at a basket of maybes and wondering whether a 7/8 inch button is the same as a 22mm one. It is, near enough. Here's how to decode the labels and buy with confidence.
What ligne actually means
Ligne, usually written as L or 'ligne' and pronounced 'leen', is a traditional button measurement. One ligne is 1/40 of an inch, or 0.635mm. It's still used by button manufacturers and many overseas suppliers, which is why a card can say 24L instead of 15mm. Pattern companies in the UK tend to use millimetres, while vintage buttons and older haberdashery cards often use imperial fractions. Three languages, one button.
A quick conversion table
The figures below are approximate, because manufacturing tolerances and rim shapes vary. Use them as a starting point, then check the actual button where you can.
| Ligne (L) | Approximate diameter | Common uses |
|---|---|---|
| 14L | 9mm | Babywear, doll clothes, delicate cuffs |
| 16L | 10mm | Shirt collars, light blouses |
| 18L | 11mm | Shirt fronts, small craft projects |
| 20L | 12.5mm | Shirts, blouses, baby knits |
| 24L | 15mm | Shirt plackets, cushions, general sewing |
| 28L | 18mm | Trousers, lightweight jackets |
| 32L | 20mm | Skirts, soft coats, bag closures |
| 36L | 23mm | Coats, heavy shirts, structured bags |
| 40L | 25mm | Coats, bags, upholstery accents |
| 44L | 28mm | Heavy coats, cushions, craft |
| 48L | 30mm | Upholstery, statement buttons |
| 60L | 38mm | Upholstery, large decorative buttons |
Imperial labels are simpler than they look. Half an inch is 12.7mm, five-eighths is about 16mm, three-quarters is about 19mm, seven-eighths is about 22mm, and one inch is 25mm. If a vintage card says 7/16 inch, that's roughly 11mm. A 5/8 inch button will usually work where a pattern asks for 15mm, but check the buttonhole before you commit.
How to measure a button at home
Use a ruler or, better, a cheap digital caliper. Measure across the widest part of the button face, not the shank. For a shank button, measure the face only; the shank sits behind and does not count towards the diameter. If the button has a pronounced rim, include the rim because that is the part that has to pass through the buttonhole. Work in millimetres. If you're matching an existing button, measure two or three others from the same garment to check consistency.
Check the buttonhole, too. A button should slip through with a little ease but not so easily that it pops open. A useful rule: buttonhole length should be the button diameter plus the button thickness plus a couple of millimetres for fabric and stitching. If you're making the buttonhole yourself, sew a test on a scrap of the same fabric first.
Shirts, coats and cushions: size pointers
Shirts and blouses: 11-15mm, about 18L-24L, is the usual range for front plackets. Cuffs often take 9-11mm; collars 9-10mm. If a UK pattern says 12mm, a 20L button at 12.5mm is usually fine, but check the buttonhole.
Coats and jackets: 20-30mm, about 32L-48L. A heavyweight wool coat may need 25-30mm, while a lightweight chore jacket can take 20-23mm. Duffle coats use toggles, so don't force a button size where a toggle belongs.
Cushions and home sewing: 15-25mm is a friendly range for envelope backs and decorative closures. Larger 30-38mm buttons make a feature of a cushion back, but check they fit through the opening or use a loop closure instead.
Bags and upholstery: 25-38mm and beyond. Here, strength matters as much as size; a pretty 15mm button won't hold a heavy bag flap.
Shopping online without the guesswork
Look for listings that give both ligne and millimetres. If only ligne is shown, convert before you buy. Read the description for shank height and hole spacing, especially if you're matching a specific pattern. Order a couple extra; dye lots vary and one spare button is a small price for peace of mind. Check the shop's returns policy. And if a listing only says 'small', 'medium' or 'large', ask for measurements. A good seller will have a ruler to hand.
At ButtonBox Supplies, we try to list sizes clearly because we know how frustrating a near-miss can be. But wherever you shop, the same rule applies: trust the millimetres, use the ligne as a cross-check, and measure the buttonhole before you commit.
