One Stop Button Shop — Sewing buttons as a | onestopbuttonshop.com
How to mark a placket: hole length of diameter plus 3 mm, centres of 75-90 mm, and a thread shank of fabric thickness plus 1-2 mm.
The buttonhole rule is fixed: cut the hole 3 mm longer than the button diameter. A 12 mm button needs a 15 mm buttonhole. The 3 mm allowance lets the button pass without straining the cloth, and it works in reverse — a lost button's size is the hole length minus 3 mm.
Spacing on a shirt front is 75-90 mm between buttons, measured centre to centre. Mark the top and bottom buttons first, then divide the distance between them evenly so no gap falls wider than 90 mm, which is where a placket starts to gape.
On narrow screens, swipe or scroll the plate sideways.
Cuffs take 1-2 buttons each, placed so the cuff closes without pulling. Most dress shirts carry 2 spare buttons in the side seam, so check there before matching anything.
The thread shank is part of the spacing job, not an afterthought: a flat sew-on button needs a shank equal to the fabric thickness plus 1-2 mm so the overlap lies flat over the underlayer. On thick cloth, skip the calculation and use a shank button, stocked from 8 to 20 mm.
Marking order matters: measure the button diameter; add 3 mm for the hole; mark centres at 75-90 mm; sew with the correct shank; then lock the thread by winding it 3-5 times around the shank and knotting through to the back. The size chart page converts any diameter to lignes, and the types page picks the attachment.
Further reading