Size converter
Convert between UK/AU, US/Canada, EU/ISO and millimetre ring sizes. Pick the system you know, enter the value, and see every equivalent.
Full reference table
Scroll for the complete range. The highlighted row matches your selection above. A dash means that system has no equivalent at that size.
| UK / AU | US / CA | EU / ISO | Diameter (mm) | Circumference (mm) |
|---|
On-screen sizer
Calibrate your screen against a bank card, then match an existing ring to a true-size circle.
Step 1: calibrate your screen
Hold a standard bank or membership card (85.60mm wide) against the rectangle below. Drag the slider until the rectangle's width exactly matches the card's width, then confirm.
Step 2: measure a ring
Place the ring flat on the screen over the circle. Adjust the diameter until the circle exactly fills the ring's inner edge, not the outside of the band. Avoid rings where a stone sits proud, as it will tilt and throw off the reading. Phone screens work well but a small screen limits how large a ring you can measure.
Print sizer sheet
Print true-size circles for UK F to Z (US 3 to about 13). Print at 100% (Actual Size) with "Fit to page" turned off, or every circle below will print the wrong size.
Calibration line: this must measure exactly 100mm once printed.
Card outline: check this against a real bank card (85.60 x 53.98mm).
If either shape above is the wrong size, open your printer settings and set scale to 100% / Actual Size, not "Fit to page".