Evenly spaced buttons make a homemade shirt, cardigan or coat look professional. This calculator spaces them along the placket, sizes the buttonholes and converts button sizes.
Even spacing
Mark the first and last button positions, then divide the distance between them:
spacing = distance from first to last button ÷ (number of buttons − 1)
For seven buttons over 20 in: 20 ÷ 6 = 3⅓ in between centers.
Where to put the first and last buttons:
- Shirts: the top button on the collar stand, the first placket button about 3 in below it, and the last one a few inches above the hem, often with one at the fullest part of the bust or chest to prevent gaping.
- Cardigans and jackets: the top button at the start of the neckline shaping, the bottom one 3 to 5 in above the hem.
- Coats: buttons usually start at chest level and stop above the hip.
If the pattern has a waistband or belt, keep a button at the waist and space the others from there.
Buttonhole length
A buttonhole must be long enough for the button to pass through easily:
buttonhole = button diameter + button thickness
A ½ in button that is ⅛ in thick needs a ⅝ in buttonhole. Domed or shank buttons need a bit more. Always sew a test buttonhole on a scrap of the same fabric with the same interfacing.
Horizontal buttonholes are stronger under strain and suit coats and waistbands; vertical buttonholes are used on shirt plackets. On a horizontal buttonhole, start the opening about ⅛ in beyond the center line toward the edge, so the button sits on the center line when fastened.
Button sizes in lignes
Buttons are often sold by ligne (L), an old unit where 1 ligne = 1/40 in, or 0.635 mm:
lignes = diameter in mm ÷ 0.635
Common sizes are 14 L (about ⅜ in) for shirts, 18 to 24 L for cardigans and blouses and 30 to 40 L for coats. The ½ in button in the example is 20 L.
Practical tips
- Buy one or two spares and sew one inside the garment.
- On knits, reinforce the button band with ribbon or interfacing so it does not stretch.
- Sew coat buttons with a thread shank so the thick fabric can sit under them.