Of every measurement you might need for a gift, ring size is the one people are least likely to know off the top of their head — which makes it both the hardest to guess and the most impressive to get right.
Method 1: Borrow an Existing Ring
If they already wear a ring on the same finger you're shopping for, this is your best option. Trace the inside edge onto paper or use a piece of string to measure the inside circumference, then compare against a printable ring sizer or jeweller's chart. Always measure a ring they wear on the same finger — sizes differ between fingers and even between hands.
Method 2: The String or Paper Strip Trick
Wrap a thin strip of paper or string around the base of their finger (snugly, not tight), mark where it overlaps, and measure the length in millimetres. Compare that circumference against the chart below.
Ring Size Conversion Chart
| US Size | UK Size | EU Size | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 5 | J | 49 | 15.7 | 49.3 |
| 6 | L½ | 51.5 | 16.5 | 51.9 |
| 7 | O | 54 | 17.3 | 54.4 |
| 8 | Q½ | 57 | 18.1 | 56.9 |
| 9 | S½ | 59 | 18.9 | 59.5 |
| 10 | U½ | 61.5 | 19.8 | 62.1 |
Always double-check with the specific retailer's chart, as small variations exist between jewellers.
Method 3: Ask a Jeweller (or Use a Sizing Ring Kit)
Most jewellers will size a ring for free, even if you're not buying that day. Alternatively, plastic ring sizer kits are inexpensive and let you (or a co-conspirator) test sizes discreetly at home.
A Word on Engagement Rings
If you're buying an engagement ring as a surprise, accuracy matters less than for everyday jewellery, because most fine jewellers offer free resizing on engagement rings within the first year. Get as close as you can using the methods above, and let the jeweller fine-tune it after the proposal.
The Bottom Line
Ring size is hard to guess and easy to get wrong by just one size — which is exactly why it's worth having on record before you need it. A few minutes with string and a ruler today saves a stressful, last-minute scramble before any future proposal, anniversary, or birthday.