UK ring sizes run from H to Z. If you are unsure, choose "Send a sizer first" on any ring page — we post a complimentary sizer and hold your piece until you confirm.
The sure way: a sizer, worn for a day
Fingers change — with temperature, with time of day, with seasons. A sizer worn through a warm evening and a cold morning tells the truth no chart can. Ours is free, posted first class, and your delivery window only begins when you confirm the size.
Converting a ring she already wears
Borrow a ring worn on the same finger and match its inside diameter to the table below. A photograph of the ring lying on a ruler, taken from directly above, works surprisingly well too — send it to hello@sertelle.co.uk and we will size it for you.
| UK size | Inside diameter | Circumference |
|---|---|---|
| H | 14.9mm | 46.8mm |
| I | 15.1mm | 47.4mm |
| J | 15.4mm | 48.3mm |
| K | 15.8mm | 49.5mm |
| L | 16.2mm | 51.0mm |
| M | 16.6mm | 52.2mm |
| N | 17.0mm | 53.5mm |
| O | 17.4mm | 54.7mm |
| P | 17.8mm | 56.0mm |
| Q | 18.2mm | 57.2mm |
| R | 18.6mm | 58.5mm |
| S | 19.0mm | 59.7mm |
| T | 19.4mm | 61.0mm |
| U | 19.8mm | 62.2mm |
| V | 20.2mm | 63.5mm |
| W | 20.6mm | 64.7mm |
| X | 21.0mm | 66.0mm |
| Y | 21.4mm | 67.2mm |
| Z | 21.8mm | 68.5mm |
A few quiet rules
- Measure at the end of a warm day for the truest fit; cold mornings run half a size small.
- Wide bands wear tighter — consider a half size up from a slim band.
- Knuckles count. If the knuckle is larger than the finger base, size for the knuckle and we will fit a discreet keeper bead on request.
- Proposing in secret? Size up rather than down — a ring that goes on can be celebrated first and fitted after.
If it still is not right
The first resize on any Sertelle ring is complimentary, whenever you need it, and made-to-order pieces include a free resize within 60 days. Read how it works on Resizing & Re-polishing.