Measure across the face
Place the button on a flat surface and measure its face across the widest relevant point. Write the result in millimetres. For an irregular shape, record width and height as well. Note thickness and attachment style separately; they are different measurements.
Understand ligne
Some suppliers use ligne, shown as L. One button ligne is 0.635 mm: multiply L by 0.635 for millimetres. Our sizing tool converts both ways. A rounded shop size may be close rather than exact, so compare the actual dimensions before buying.
Keep the context
A button for a shirt, coat or decorative card has a different job. Keep the garment, buttonhole and care label in the record. A diameter conversion does not confirm that the button fits the closure.
Do a loose fit check
With the garment supported, see whether the replacement passes through the existing hole without forcing it. Check the supplier’s stated dimensions, quantity and underside. Keep an existing spare with the notes if you have one.
Further learning
Technical details checked against these resources on 9 October 2026. Our planning advice and project layouts are original.
Reviewed 9 October 2026 · Suggest a correction
