Buttonhole Spacing Calculator — Even Placement

Divide the available placket length (minus the first and last button positions) by the number of gaps between buttons. For 5 buttons, there are 4 gaps. This gives even spacing between each buttonhole.

The accepted rule is button diameter plus button thickness plus about 3mm (1/8 inch) for ease. This calculator multiplies the diameter by a length factor (1.1 for flat buttons, 1.2-1.3 for domed), adds 3mm ease, then adds your shank allowance for button thickness. A thicker or domed button therefore needs a longer buttonhole so it can pass through easily.

The first button is typically 1.5-3cm from the top edge (neckline or collar). The last button is usually 2-5cm from the bottom hem. On shirts, the first button is at the collar band; on dresses, it can be at the neckline or bust.

The overlap (the button extension that sits beyond the buttonhole) should be at least half the button diameter plus a little extra — this calculator adds 2.5mm. For a 15mm button, allow at least 10mm overlap. The button is centred on the overlap, and the buttonhole is centred on the button band.