The length of your test buttonhole should be equal to half the circumference plus 1/8 inch. If your button is very thick, you may need to increase the size a little more. Test the size before making any buttonholes on your garment (Figure 1).

What size buttonhole is needed for a button?

Size Matters

The rule of thumb is that the buttonhole is 1/8″ (3 mm) bigger than the button. Hence, 1/2″ button uses 5/8″ buttonhole (1.25 cm button uses 1.6 cm buttonhole)

How to measure a button hole?

Measure your button by wrapping twill tape or seam binding around the button's widest point and pinning the tape together. The button width will be half of this measurement. To determine your buttonhole length, add ⅛” to the button width. If your buttons are thick add a little more than ⅛” to the length.