Ring Size Calculator
Find your ring size from finger circumference or diameter measurements in US, UK, and EU formats.
Formula
Ring size mapped from circumference using standard sizing chart
- Measure at the widest part of the finger (knuckle if wider than base).
- Measure in the afternoon when fingers are slightly larger.
- UK size letters: A (smallest) → Z (largest), with half-sizes.
55 mm circumference
Inputs
- Measure: circumference
- Measurement: 55 mm
55 mm circumference → US size 7. Diameter = 55/π ≈ 17.5 mm.
Frequently asked questions
How do I measure my ring size?
Wrap a thin strip of paper around your finger, mark where it meets, and measure the length in mm.
What time of day should I measure?
Afternoon is best — fingers swell slightly from activity and temperature during the day.
What if I'm between sizes?
Size up for wider bands. Size down for comfort-fit rings (which feel smaller inside).
Does temperature affect ring size?
Yes — cold makes fingers shrink, heat makes them swell. Measure at room temperature.