Ring Size Measurer

Find your ring size without printing anything. Calibrate with a bank card, lay a ring you already own over the circle, and size it to match — get US, UK, EU and Japanese sizes instantly.

How to measure your ring size

Calibrate once with a bank card, then take a ring that already fits the finger you're sizing. Lay it flat on the screen over the coloured circle and drag the slider until the circle exactly fills the inside of the ring. The tool reads the inner diameter and shows your size in every major system. Measure the inner hole, not the metal's outer edge.

Calibrate once, size accurately. Screen calibration is shared with the Actual Size Ruler and Eye Test. Nothing is uploaded — it all runs in your browser. Fingers swell in heat and shrink in cold, so measure at the end of the day at room temperature for the best fit.

Ring sizes around the world

The US/Canada use numbers, the UK/Australia use letters, the EU/ISO standard is simply the inner circumference in millimetres, and Japan/China use their own numeric scale. One measurement here gives you all four, so you can order confidently from any shop.

Frequently asked questions

How do I measure my ring size online?

Calibrate to a bank card, lay a ring that fits on the screen, and size the circle to the ring's inner hole. The inner diameter maps to US, UK, EU and JP sizes.

Is measuring an existing ring accurate?

Yes — you're matching a known good fit, which is one of the most reliable home methods. Avoid browser zoom and measure the inner hole.

What if I don't have a ring that fits?

Wrap a paper strip around the finger, mark the overlap, and measure that length in mm with our ruler — that's the circumference. Or just slide to a diameter to convert between systems.

Do ring sizes differ by country?

Yes. US numbers, UK letters, EU millimetres and Japanese numbers all differ — this tool shows all of them from one measurement.

More free tools

Measure: Actual Size Ruler · Vision: Eye Test · See all Alienated Tools.