Ring Size Calculator — EU, US, UK & Japan Sizes
Wrap a thin strip of paper around your finger, measure its length (inner circumference) or measure the inner diameter of a ring that already fits, then enter the value here to get your size in every major standard: EU/ISO, US/Canada, UK/Australia and Japan.
Measurement type
mm
Inner circumference in mm, rounded to the nearest whole number
- 1
Inner circumference
52 - 2
EU ring size
52Inner circumference in mm, rounded to the nearest whole number.
How does this calculator work?
Measure the inner circumference of your finger in mm (strip-of-paper method), then convert: EU size = that circumference rounded to the nearest whole number; US size = (circ − 36.5) ÷ 2.55; UK = letter based on 1.25 mm steps from A at 37.5 mm; Japan = circumference − 40.
Formula
How this is calculated
The EU/ISO standard is the simplest: the ring size equals the inner circumference in millimetres, rounded to the nearest whole number. A size 52 ring has an inner circumference of 52 mm (inner diameter ≈ 16.6 mm). Every other sizing system uses a linear mapping from that same circumference.
The US/Canada size is derived as (circumference_mm − 36.5) ÷ 2.5527, where US size 0 anchors at 36.5 mm circumference and each full size step equals 2.5527 mm. The UK and Australian system uses letters A through Z, with UK A starting at about 37.5 mm inner circumference and each letter representing a 1.25 mm step. Japanese sizes start at 1 (≈ 41 mm circumference) and increase by roughly 1 mm per step, so Japan size ≈ circumference − 40.
To measure at home: cut a thin strip of paper about 15 cm long, wrap it snugly (not too tight — you should be able to slide a ring past your knuckle) around the widest part of the base of the finger you plan to wear the ring on, mark where the strip overlaps, and measure the length in mm. That length is your inner circumference. Finger size can vary up to 1–2 sizes through the day (larger when warm and swollen, smaller when cold), so measure mid-day at room temperature.
Frequently asked questions
Wrap a thin strip of paper around the base of your finger at the widest point (usually just below the knuckle). Mark where it overlaps, lay it flat and measure in millimetres — that is your inner circumference. Divide by π (≈ 3.1416) for the inner diameter. Measure mid-day when your fingers are at their normal size.
Different standards developed independently. The EU/ISO system uses the inner circumference directly in mm, the US system uses an arbitrary numeric scale, the UK uses letters, and Japan uses its own numeric scale. The underlying measurement is the same — only the notation differs.
Choose the larger size if your knuckle is wide or if you plan to wear the ring all day — rings are easier to remove when slightly loose. If the ring will be thin (wedding band style) and the stone is heavy, lean toward a snugger fit. Many jewellers can resize a ring up or down by half a size.
Also known as
TG we-Calculate Editorial Team. (2026). Ring Size Calculator — EU, US, UK & Japan Sizes [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/ring-size-calculator
TG we-Calculate Editorial Team. "Ring Size Calculator — EU, US, UK & Japan Sizes." TG we-Calculate. 2026. https://we-calculate.com/calculator/ring-size-calculator.
TG we-Calculate Editorial Team, "Ring Size Calculator — EU, US, UK & Japan Sizes," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/ring-size-calculator
@misc{wecalculate_ring_size_calculator, title = {Ring Size Calculator — EU, US, UK & Japan Sizes}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/ring-size-calculator}}, year = {2026}, note = {TG we-Calculate} }
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