Convert ring sizes between EU/ISO, US, UK and Japanese systems. Enter a circumference, diameter, or a size you already know.
EU / ISO
54
US
6¾
UK
N
JP
14
Calculator
Ring sizes
EU 54
US
6¾
UK
N
JP
14
EU / ISO
54
US
6¾
UK
N
JP
14
Diameter
17.19 mm
Circumference
54 mm
To-scale ring
Wrap a strip of paper or thin string around the base of your finger and mark where it overlaps — that length is your inner circumference in mm. Alternatively, place a ring that fits over the circle below and match the inner edge to the scale.
How ring size systems work
EU/ISO 8653 is the simplest: the size number equals the inner circumference in millimetres. A ring with a 54 mm inner circumference is EU size 54. US sizes use a linear scale anchored to published charts — each full US size adds about 2.55 mm of circumference. UK sizes use letters A through Z, with half sizes denoted by ½, and each letter step adds roughly 1.3 mm.
Japanese sizes are also circumference-based but with a different offset — JP 14 ≈ 54 mm circumference. To convert accurately, measure your inner circumference in mm and let this tool do the rest.
Which ring size system is most widely used?
EU/ISO sizing is used across continental Europe and increasingly internationally. US sizing is standard in North America. UK / Ireland / Australia / New Zealand share the letter system. Japan uses its own numerical scheme.
How do I measure my ring size at home?
Wrap a narrow strip of paper around your finger, mark the overlap, and measure that length in mm — that is your inner circumference. Alternatively, measure the inner diameter of a ring that fits and enter it here.
Why does the size vary between my fingers?
Finger size changes with temperature, time of day and hydration. Measure in the evening when fingers are at their largest, and measure the specific finger you plan to wear the ring on.
Results are estimates. Verify with a professional for important decisions.
About this calculator
This converter translates a ring measurement into all four major sizing systems at once: EU/ISO 8653 (circumference in mm), US/Canada (numeric), UK/Australia (letters), and Japan (numeric). Enter an inner circumference, a diameter, or a size you already know from any system to get the equivalents instantly.
How to read your results
The result panel shows the same physical ring size expressed in each system. EU equals the inner circumference in millimetres exactly, so EU 57 means the inner circumference is 57 mm. US and JP sizes are numbers; the UK/Australia system uses letters with optional half-steps (for example N or N½). Ring sizing varies by country and brand and uses fine increments; treat conversions as approximate and confirm with a jeweler.
Worked example
Enter an inner circumference of 57 mm (EU mode).
EU 57, US 8, UK P, JP 17. The inner diameter is 18.1 mm. This is one of the most common ring sizes worldwide.
Frequently asked questions
What is EU ring size and why does it equal the circumference?
EU ring size follows ISO 8653, which defines size as the inner circumference of the ring in millimetres. A ring marked EU 57 has an inner circumference of exactly 57 mm, so no formula is needed — the number is the measurement.
How do I measure my ring size at home?
Wrap a thin strip of paper snugly around the base of the finger you want to wear the ring on. Mark where the strip overlaps, then measure the length in millimetres — that is your inner circumference. Enter it here as EU or circumference to get all four systems.
Why does my US size come out as a fraction like 6.75 or 8.25?
US sizing uses quarter increments (for example 7, 7¼, 7½, 7¾) because finger circumferences do not fall on exact whole-number US sizes. The calculator rounds to the nearest quarter step, which is the precision jewelers actually stock.
Are UK and Australian ring sizes the same?
Yes. The UK and Australian letter system is identical — the same letter chart is used in both countries. New Zealand also follows this system.
Why might a ring purchased abroad not fit even when the size matches?
Ring width and shape affect perceived fit: a wide band feels tighter than a narrow one at the same size. Temperature, time of day, and dominant-hand swelling also change finger circumference slightly. Always try a ring on before purchasing or ask a jeweler to use a mandrel for a precise fitting.
How it's calculated
All conversions are grounded in the physical inner circumference of the ring in millimetres, as defined by ISO 8653. EU size is the circumference directly. Diameter is derived as circumference divided by π. The US/Canada size uses a linear model anchored to published reference values (US 0 = 36.537 mm, each full size adds 2.5535 mm), solved for the nearest quarter step. The UK/Australia letter system uses a lookup table of circumference values derived from the Wikipedia ring-size comparison chart (A = 37.8 mm through Z = 69.5 mm, half sizes interpolated as midpoints). The Japanese system applies a linear offset: JP size = round(circumference − 39.84 mm), anchored so JP 1 = 40.84 mm and verified at JP 14 = 54 mm and JP 17 = 57 mm.
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