Buttonhole Size Calculator
Buttonhole length from the button itself.
Calculate buttonhole length from a button's diameter and thickness, so domed and shanked buttons still pass through.
Buttonhole length
1.02"
26.0 mm
Thickness matters because the button turns edgewise to pass through, so a hole cut to the diameter alone binds and wears out. Test on a scrap of the same fabric with the same interfacing before committing — fabric thickness changes how a buttonhole behaves.
How the Buttonhole Size Calculator works
A buttonhole has to be longer than the button is wide, because the button passes through edgewise. The rule is diameter plus thickness, and thickness is the part people forget — a flat shirt button and a domed coat button of the same diameter need noticeably different holes.
Also known as: buttonhole length calculator · button hole size chart
Diameter is not enough
A buttonhole must be longer than the button is wide, because the button passes through edgewise rather than face-on. The length needed is the diameter plus the thickness, plus a small amount of ease.
Thickness is the term people drop, and it is why a flat shirt button and a domed coat button of identical diameter need noticeably different holes. A hole cut to the diameter alone binds, and binding is what wears a buttonhole out.
An eighth of an inch of ease is usual. Less on a fine fabric with a small button; more on a thick coat where the fabric itself resists the button turning.
A worked example
A three-quarter inch button, an eighth of an inch thick, with an eighth of ease: 0.75 + 0.15 + 0.125, so a buttonhole just over an inch long.
The same diameter in a domed button a third of an inch thick needs 1.2 inches — a fifth longer for a button that looks the same size on the card. Buttons are also sold in ligne, where 40 ligne is one inch, so a three-quarter inch button is a 30 ligne.
Where the answer misleads
Fabric behaviour changes what works. The same buttonhole in a stable interfaced placket and in an unstable knit behave completely differently, and the knit will stretch the hole in use. Test on a scrap of the actual fabric with the actual interfacing before committing to a length.
Automatic buttonholers that measure from the button itself are usually reliable but tend to size for a flat button, so a domed or shanked one may still need the length increasing manually.
Finally, a buttonhole that is slightly too long is a worse problem than one slightly too short — a short one can be unpicked and extended, while a long one lets the button slip and cannot be shortened without redoing it.
Frequently asked questions
How long should a buttonhole be?
The button's diameter plus its thickness, plus about an eighth of an inch of ease. A three-quarter inch button that is an eighth thick needs a buttonhole of about one inch.
Why does thickness matter?
Because the button turns edgewise to pass through. A thick or domed button presents more than its diameter as it goes, so a hole cut to the diameter alone binds — which is what wears the buttonhole out.
What about shank buttons?
Measure the widest part of the button head and treat the shank as thickness. Shank buttons generally need slightly more ease because the shank has to sit in the hole while the head passes through.
Should I test first?
Always, on a scrap of the same fabric with the same interfacing. Fabric thickness and stretch change how a buttonhole behaves, and a hole that works in calico can be tight in the actual cloth.