How do I calculate buttonhole spacing?

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.

How long should a buttonhole be?

A buttonhole should be the button diameter plus 3mm for ease, multiplied by a factor of 1.1 for flat buttons. Thicker or domed buttons need a factor of 1.2-1.3. The buttonhole must be large enough for the button to pass through easily.

Where should the first and last buttons be?

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.

How wide should the button overlap be?

The overlap (the fabric that extends beyond the buttonhole) should be at least half the button diameter plus 2mm. 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.

SewCalcs

Buttonhole Spacing Calculator — Even Placement

Calculate even buttonhole placement, spacing and buttonhole length for garments.

Placket Length

Total length of button band

Number of Buttons

Enter the number of buttons

Button Diameter

Measured across the widest point

First Button Position

Distance from top edge

Last Button Position

Distance from bottom edge

How We Calculate This

This calculator divides the usable placket length evenly between buttons and calculates the correct buttonhole length based on button size.

The formula

Spacing = (Placket length - First position - Last position) ÷ (Buttons - 1)

Buttonhole length = (Button diameter × Length factor) + 3mm

Overlap = (Button diameter ÷ 2) + Shank allowance

Frequently Asked Questions

Last updated: March 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.