Ring Size Calculator
Find your ring size from a quick finger measurement, or convert a known size between US, UK, EU and Japanese systems — all in one place.
Measure your finger
Wrap a strip of paper or string around your finger, mark where it overlaps, and measure the length in millimetres — that's your circumference. Or measure the inside diameter of a ring that fits.
Your ring size
US 7
Closest standard size to your measurement.
US / Canada
7
UK / Australia
O
EU / ISO
54
Japan / China
14
Diameter
17.3 mm
Circumference
54.4 mm
Measure at the end of the day when fingers are warm, and size for the widest knuckle the ring must pass over. Wide bands fit tighter — go up a half size for bands over 6 mm.
Measure a ring you already own
No tape measure needed. Calibrate your screen with any bank card, then resize the circle to match a ring that fits the right finger. We read the size straight off the screen.
1Calibrate your screen
Hold a credit, debit or ID card flat against the screen and drag the slider until the blue box is exactly the same width as the card.
Calibrated scale: 3.79 pixels per mm.
2Match your ring
Place a ring on the screen and resize the circle until it sits just inside the band's inner edge.
US 7
UK O · EU 54 · JP 14
Inside diameter ≈ 17.4 mm (54.8 mm around)
Print a ring sizer
Prefer paper? Print our to-scale ring sizer, then drop a ring you own over the circles — the one that frames the band's inside is your size. It includes a check bar so you can confirm your printer scaled correctly.
Important: in the print dialog set Scale to 100% and turn off "Fit to page", then measure the check bar — it must be exactly 85.6 mm (3.37 in) wide.
No ring to measure? Use the string method
Step 1. Wrap a strip of paper or string snugly around the base of your finger.
Step 2. Mark where it overlaps, then lay it flat and measure the length in millimetres.
Step 3. Enter that circumference in the calculator above to get your ring size.
Ring size conversion chart
The full international ring size chart, matched to the band's inside diameter and circumference in millimetres.
| US / Canada | UK / Australia | EU / ISO | Japan / China | Diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.0 mm | 44.0 mm |
| 3.5 | G | 45 | 5 | 14.4 mm | 45.5 mm |
| 4 | H | 47 | 7 | 14.8 mm | 46.8 mm |
| 4.5 | I | 48 | 8 | 15.2 mm | 48.0 mm |
| 5 | J½ | 49 | 9 | 15.7 mm | 49.3 mm |
| 5.5 | L | 51 | 10 | 16.1 mm | 50.6 mm |
| 6 | M | 52 | 11 | 16.5 mm | 51.9 mm |
| 6.5 | N | 53 | 13 | 16.9 mm | 53.1 mm |
| 7 | O | 54 | 14 | 17.3 mm | 54.4 mm |
| 7.5 | P | 56 | 15 | 17.7 mm | 55.7 mm |
| 8 | Q | 57 | 16 | 18.2 mm | 57.0 mm |
| 8.5 | Q½ | 58 | 17 | 18.6 mm | 58.3 mm |
| 9 | R½ | 60 | 18 | 19.0 mm | 59.5 mm |
| 9.5 | S½ | 61 | 19 | 19.4 mm | 60.8 mm |
| 10 | T½ | 62 | 20 | 19.8 mm | 62.1 mm |
| 10.5 | U½ | 64 | 22 | 20.2 mm | 63.4 mm |
| 11 | V½ | 65 | 23 | 20.6 mm | 64.6 mm |
| 11.5 | W½ | 66 | 24 | 21.0 mm | 65.9 mm |
| 12 | X½ | 68 | 25 | 21.4 mm | 67.2 mm |
| 12.5 | Z | 69 | 26 | 21.8 mm | 68.5 mm |
| 13 | Z½ | 70 | 27 | 22.2 mm | 69.7 mm |
Shopping for a birthstone ring? Browse our birthstone jewellery guide or value a stone with the diamond price calculator.
Frequently Asked Questions
How do I measure my ring size at home?
What is the average ring size?
How do US, UK and EU ring sizes compare?
Should I size up for a wide band?
How accurate is an online ring size calculator?
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