Ring Size Calculator: Measure, Convert & Size a Ring On Screen

Wrap a strip of paper or string around the base of your finger, mark where it overlaps, and measure the length in millimetres. That's your circumference: enter it in Measure mode to get your US, UK, EU, German, Japanese and Swiss sizes at once. Measure at the end of the day, and choose the larger size if you're between two.

Use the on-screen sizer. Hold any bank or ID card against the screen to calibrate it, then lay a ring that fits on the circle and adjust until it touches the inside edge. You can also print the ring sizer, which has true-scale circles and a cut-out paper strip.

Borrow a ring they wear on the same finger and size it on screen or against the printable circles, or measure its inner diameter in millimetres and enter it in Measure mode (Diameter). If you have to guess, the average is about US 6–7 for women and US 9–10 for men; round up rather than down.

A US 7 ring has an inner diameter of about 17.3 mm and an inner circumference of 54.4 mm. That's a UK/Australian N½, EU/ISO 54, German 17.25, Japanese 14 and Swiss 14.5.

UK sizes run from A to Z with half sizes, then Z+1 upwards. Each whole letter adds about 1.3 mm of circumference, roughly half a US size. Common conversions are UK J½ ≈ US 5, L½ ≈ US 6, N½ ≈ US 7, P½ ≈ US 8, R½ ≈ US 9 and T½ ≈ US 10. Pick UK in Convert mode to see any letter in every other system.

Yes. Bands wider than about 6 mm sit tighter because more metal touches the finger. Go up about half a size for 6–8 mm bands and three quarters of a size for 8 mm and wider. Choose the band width in Measure mode and it's added for you.

Measure both the base of the finger and the knuckle. The ring has to pass over the knuckle, so choose a size between the two. Tick the knuckle option in Measure mode and the calculator sizes halfway towards your knuckle. Rings with sizing beads or hinged shanks can help too.

Yes, ring sizes are unisex: a US 9 is the same size whoever wears it. Men's rings simply tend to be larger (about US 8–12) and wider, so the band-width adjustment matters more.

No. EU (ISO 8653) sizes are the inner circumference in millimetres, so EU 54 is 54 mm around. Japanese sizes use a separate scale where each size adds about one third of a millimetre of diameter; EU 54 is about JP 14. The calculator converts between them from the exact circumference.

Most gold, silver and platinum bands can be resized by a jeweller about two sizes up or down. Eternity bands, tension settings, tungsten, titanium, ceramic and many engraved or patterned rings usually can't, so confirm your size before ordering those.

Yes. It's free with no sign-up and runs entirely in your browser. Your measurements and screen calibration are stored only on your own device and are never uploaded.