Ring size converter
Convert diameter and circumference into FR, US and UK ring sizes.
- Instant
- Free
- Private (processed locally)
- No sign-up
The right ring size, without a sizer
Buying a ring online or abroad means juggling FR, US and UK sizes. From a simple measurement in millimetres, this tool finds your size in all three systems.
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Measure in mm
Inner diameter, or circumference (finger wrap).
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Enter the value
The tool finds the closest row.
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Read the sizes
FR, US and UK, with diameter and circumference.
Reference correspondences
| Ø (mm) | Circ. (mm) | FR | US | UK |
|---|---|---|---|---|
| 15.7 | 49.3 | 49 | 5 | J½ |
| 16.5 | 51.9 | 52 | 6 | L½ |
| 17.3 | 54.4 | 54 | 7 | O |
| 18.1 | 57.0 | 57 | 8 | Q |
Circumference = diameter × π. The FR size equals the finger circumference in mm. Measure at the end of the day for reliability.
Frequently asked questions
How do I measure my ring size?
Two methods: measure the inner diameter of a ring that fits (in mm, edge to edge), or wrap a strip around your finger to read the circumference in mm. Enter either one: the tool finds the matching size.
What is the French size?
In France, ring size equals the finger circumference (inner circumference) in millimetres. A FR 54 size means a 54 mm circumference. It is simple and direct, unlike US numbers or UK letters.
How do I go from diameter to circumference?
The circumference equals the diameter times π (3.1416). An inner diameter of 17.3 mm gives a circumference of about 54.4 mm, i.e. size FR 54, US 7 and UK O.
When should I measure my finger?
At the end of the day and at normal temperature: fingers swell with heat and effort, and shrink in the cold. Measure several times and choose a size that passes the knuckle without being permanently tight.