Ring sizes are circumference measurements, but the finger is not a cylinder. A wider band covers more of the finger's curved surface, which increases friction and reduces the space the ring has to move.
The rule of thumb
| Band width | Add to size |
|---|---|
| Up to 3 mm | Nothing |
| 4–5 mm | ¼ size |
| 6 mm | ½ size |
| 8 mm | ¾ to 1 full size |
| 10 mm+ | 1 full size, and consider comfort fit |
Why it happens
Skin under a wide band cannot bulge around the edges the way it can under a narrow band. The ring effectively sits on a larger cross-section of the finger. Add heat, salt or a long flight and the difference becomes obvious.
Comfort fit changes the number again
A comfort-fit interior is rounded, so only the centre of the band's inside touches the finger. At the same size it feels looser than a flat interior — roughly a quarter size. If you are moving from a flat 4 mm band to a comfort-fit 6 mm band, the two effects partly cancel.
Stacking rings
Three 2 mm rings on one finger behave like a 6 mm band: they cover the same surface and feel tighter. Size for the stack, not for one ring, and consider a slightly larger size for the middle ring so the set does not bind.
What to do if you already ordered
Gold and platinum rings can usually be sized up by a quarter to half a size without visible damage. Silver rings are better exchanged. Eternity bands and rings with stones all the way around are difficult to resize — which is why we confirm the size in writing before casting.
The people who cut the stones and set the rings. We publish what we can verify on our own bench, and link to the certificate or the guide when a number needs a source.
