Czech jewellers — like most of Europe — size rings by inner circumference in millimetres (EU sizing), while US and UK systems use numbers and letters. Here's the conversion at a glance, and the sneaky part: how to learn their size without asking.
The conversion chart
| EU (mm) | US | UK |
|---|---|---|
| 47 | 4 | H½ |
| 48 | 4.5 | I½ |
| 49 | 5 | J½ |
| 50.5 | 5.5 | K½ |
| 52 | 6 | L½ |
| 53 | 6.5 | M½ |
| 54 | 7 | N½ |
| 55.5 | 7.5 | O½ |
| 57 | 8 | P½ |
| 58 | 8.5 | Q½ |
| 59.5 | 9 | R½ |
Approximate equivalents — systems don't align perfectly, so always confirm with the jeweller.
Three ways to find their size in secret
1. Borrow a ring they wear on the same finger (left ring finger ideally) and take it to any jeweller — or trace its inner circle on paper. 2. Recruit an ally: a friend or sister can spark a casual ring-try-on at a market stall. 3. The sleep-of-the-brave method: a piece of string around the finger while they sleep — legendary, occasionally successful, frequently busted.
When in doubt, size up
A slightly loose ring goes on smoothly during the proposal (cold hands shrink fingers!) and resizing down afterwards is routine — most jewellers include one free resize. A too-small ring stuck at the knuckle mid-proposal is the scenario we're all avoiding.
Or skip the guessing entirely
Propose with a placeholder band and choose the real ring together afterwards — increasingly popular, zero sizing risk, and the ring-shopping date becomes part of the story. Our Prague ring-buying guide covers where to go.