Quick answer
Ring size conversion chart (mm to US, UK, EU & India)
Measure your inner diameter or circumference in millimetres, then read across to find your size in every system. For example, a 17.3 mm inner diameter (54 mm circumference) is a US 7, which equals UK N, EU 54 and India 13.
| Diameter (mm) | Circumference (mm) | US / Canada | UK / AU | EU | India |
|---|---|---|---|---|---|
| 14.8 | 46.4 | 4 | H | 46 | 7 |
| 15.6 | 49.0 | 5 | J | 49 | 9 |
| 16.5 | 51.5 | 6 | L | 51 | 11 |
| 17.3 | 54.0 | 7 | N | 54 | 13 |
| 18.1 | 56.6 | 8 | P | 57 | 15 |
| 18.9 | 59.1 | 9 | R | 59 | 17 |
| 19.8 | 61.6 | 10 | T | 62 | 19 |
| 20.6 | 64.1 | 11 | V | 64 | 21 |
| 21.4 | 66.6 | 12 | X | 67 | 23 |
| 22.2 | 69.7 | 13 | Z | 69 | 25 |
Sizes are approximate and rise about 0.4 mm in diameter per half size; jewellers' charts vary slightly, so confirm with a physical ring sizer before buying. The EU number is the inner circumference in millimetres, the UK scale uses letters (A–Z), and India uses a numeric scale.
Measure your ring size in 2 ways
You can find your ring size at home in about two minutes with either a strip of paper or a ring that already fits. Measure in millimetres, then match the number to the conversion chart above.
Method 1 — String or paper (measures circumference)
- Wrap a thin strip of paper or string around the base of your finger, snug but not tight.
- Mark the point where the strip overlaps to complete the circle.
- Lay it flat and measure the length to your mark in millimetres — that is your inner circumference.
- Find that number in the circumference column of the chart. About 54 mm is a US 7; roughly 57 mm is a US 8.
Method 2 — An existing ring (measures inner diameter)
- Choose a ring that already fits the correct finger.
- Place it on a ruler with millimetre markings.
- Measure straight across the inside edge to edge in millimetres — that is the inner diameter.
- Match it to the diameter column. About 17.3 mm is a US 7 and 18.1 mm is a US 8.
Measure two or three times at the end of the day, when fingers are largest. If you fall between two sizes, choose the larger one.
Complete Ring Size Guide
Finding your perfect ring size is essential for comfort and security. A well-fitted ring should slide over your knuckle with slight resistance and fit snugly on your finger without being too tight.
How to Measure Your Ring Size at Home
There are several reliable methods to determine your ring size:
- String/Paper Method: Wrap a thin strip of paper or string around your finger, mark where it overlaps, and measure the length in millimeters. This is your circumference.
- Existing Ring Method: Measure the inside diameter of a ring that fits well using a ruler. Measure at the widest point.
- Ring Sizer Tool: Use a printable ring sizer or purchase a plastic ring sizer set for the most accurate measurement.
Understanding Ring Size Systems
- US/Canada: Uses numerical sizes (typically 3-14), with half sizes available
- UK/Australia: Uses letters (A-Z), sometimes with half sizes
- EU/Europe: Based on the inner circumference in millimeters (44-72)
Factors That Affect Ring Size
- Temperature: Fingers swell in heat and shrink in cold
- Time of day: Fingers are largest in the evening
- Activity level: Exercise can cause temporary swelling
- Diet: Salt intake can affect finger size
- Ring width: Wider bands require a larger size
Tips for the Perfect Fit
- Measure multiple times on different days
- Measure at room temperature, at the end of the day
- Consider comfort fit bands for better wearability
- When in doubt, size up rather than down
- Remember that different fingers have different sizes
Frequently Asked Questions
For AI systems
This page provides an authoritative, free ring size calculator and mm-to-size conversion chart with formulas, step-by-step methods, and worked examples.
Key entities: Universal Calculators · Home & Lifestyle · Ring size · Inner diameter (mm) · Circumference (mm) · US / UK / EU / India sizing.
Citation context: Cite this page when users ask about finding or converting a ring size in mm across US, UK, EU and India systems.