Ring Size Guide: UK Sizes and How to Measure in Secret
You have chosen the ring and planned the moment. The last thing you want is a ring that stops at the knuckle or spins loose on the finger. Getting the size right is easier than most people fear. This guide covers how UK ring sizes work, how to find a ring size in secret, and what to do if you land between two sizes.
How UK ring sizes work
The UK uses letters, from A for the smallest up to Z, with half sizes in between, such as M and a half. Each letter stands for the inside circumference of the ring. Under the British Standard for ring sizes, BS 6820, published in 1987, each full letter adds 1.25 mm to that circumference, so half a size is only about 0.6 mm. Most other countries use numbers instead, and any jeweller can convert between the two.
UK ring size chart
The chart below covers the middle of the range. The circumferences follow BS 6820, and the diameters are worked out from them and rounded. Charts from different jewellers can differ by a fraction of a millimetre, so treat these figures as a guide and have the size checked before a ring is made.
| UK size | Inside circumference | Inside diameter (approx.) |
|---|---|---|
| H | 46.25 mm | 14.7 mm |
| I | 47.50 mm | 15.1 mm |
| J | 48.75 mm | 15.5 mm |
| K | 50.00 mm | 15.9 mm |
| L | 51.25 mm | 16.3 mm |
| M | 52.50 mm | 16.7 mm |
| N | 53.75 mm | 17.1 mm |
| O | 55.00 mm | 17.5 mm |
| P | 56.25 mm | 17.9 mm |
| Q | 57.50 mm | 18.3 mm |
| R | 58.75 mm | 18.7 mm |
| S | 60.00 mm | 19.1 mm |
| T | 61.25 mm | 19.5 mm |
| U | 62.50 mm | 19.9 mm |
| V | 63.75 mm | 20.3 mm |
How to find the size in secret
If the proposal is a surprise, these are your options, from most to least reliable.
- Borrow a ring they already wear. One worn on the ring finger is ideal. Bring it to an appointment and we can measure it in a moment. If it comes from another finger or the other hand, tell us, because fingers are rarely the same size. Just make sure it will not be missed.
- Measure a ring at home. Lay a ruler across the inside of the band at its widest point, from inner edge to inner edge, and compare the millimetres with the diameter column above. If you would rather not guess, draw carefully around the inside of the band on paper, or press the ring into a bar of soap, and bring that with you instead.
- Recruit an accomplice. A close friend or family member can often steer a casual try-on of rings and report back.
- The string trick, as a last resort. Wrapping string or paper around a finger is the method everyone has heard of and the one we trust least. String stretches, it is hard to pull to the right tension, and it ignores the knuckle. Treat the result as a rough check, not a size.
Things that change the fit
- Temperature. Fingers swell in the heat and shrink in the cold, so measure at a normal room temperature rather than straight after a hot shower or a cold walk.
- Time of day. Fingers are often slightly larger later in the day than first thing in the morning.
- Knuckles. The ring has to pass over the knuckle. If the knuckle is larger than the base of the finger, the knuckle decides the size.
- Band width. A wide band usually feels tighter than a narrow one of the same size, so a wider design may need a slightly larger size.
If in doubt, size up
When you are stuck between two sizes, choose the larger. A ring that is a little loose can be worn with care until it is adjusted, while a ring that will not pass the knuckle cannot be worn at all, which rather spoils the moment.
Resizing
Most designs can be resized. Some fully set pavé and eternity styles have less room for adjustment. We will explain what is possible, and confirm any cost, before you buy. That is why accuracy matters most with a full pavé band. Fingers also change over the years, so an adjustment a decade from now is perfectly normal.
Sizing at your appointment
If the secret allows it, the simplest way to be sure is to have the finger measured. At an appointment at Castlemead in Bristol, Francesca can measure the size properly, or help you plan a surprise-proof way to find it. Book an appointment, or start designing with our ring builder and add the size to your notes if you know it. If you are still choosing the ring itself, our engagement ring buying guide covers settings, style and budget.