Complete 2026 ring size chart with diameter and circumference in millimetres โ UK, US, EU, French and Japanese conversions, proportional circle diagrams, MM calculator and expert measurement tips.
| ๐ Diam. MM | ๐ Diam. CM | ๐ Diam. Inch | โญ Circ. MM | โญ Circ. CM | โญ Circ. Inch | ๐ฌ๐ง UK | ๐บ๐ธ US | ๐ฉ๐ช EU | ๐ซ๐ท French | ๐ฏ๐ต Japan | Category |
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Wrap a thin paper strip around the base of your ring finger. Mark the overlap point. Lay the strip flat and measure in mm with a ruler โ this gives your circumference in mm.
Wrap a piece of string around your finger, mark the overlap, then measure the string in mm against a ruler. Works well for larger fingers where paper strips may be too stiff.
Use digital calipers to measure the inner diameter in mm of an existing ring. This is the most precise method โ accurate to 0.1mm. Enter the result in the calculator above.
If you have the circumference in mm and want the diameter: d = C รท 3.1416. Conversely, d ร 3.1416 = C. Use either measurement in the table above.
Look up your mm reading in the Circ. MM or Diam. MM column of the chart. If between two sizes, always use the larger โ it's easier to tighten a slightly loose ring than force on a tight one.
Once you have the MM values, read across the same row for UK letter, US number, EU, French or Japanese size. The EU size is literally your circumference rounded to the nearest whole mm.
MM is the universal standard for ring sizing. Both the UK (BS EN 28653) and EU (ISO 8653) define sizes in mm โ using mm removes all ambiguity when ordering from any country.
The EU ring size is simply the inner circumference rounded to the nearest mm. So if your circumference is 51.2mm, your EU size is 51. No conversion needed โ read the number directly.
Adjacent UK ring sizes differ by approximately 0.4mm in diameter and 1.3mm in circumference. If your measurement sits between two sizes, round up โ never down.
Fingers can fluctuate by up to 0.5mm in diameter between morning and evening, or between cold and warm temperatures. Always measure in the afternoon at room temperature for the most reliable reading.
A digital caliper (under ยฃ10) gives diameter readings accurate to 0.1mm. Far more precise than a paper strip. Measure the inner diameter of an existing well-fitting ring for the fastest, most accurate result.
When ordering from international sites, always quote your inner circumference in mm rather than a size letter or number โ the universal mm value is understood by every jeweller worldwide with no ambiguity.
A ring band wider than 6mm will feel tighter on the finger than a standard 2โ3mm band, even at the same mm diameter. Go up 0.4โ0.8mm in diameter (half to one UK size) for wide engagement or wedding bands.
Take your circumference or diameter measurement morning, afternoon and evening on the same day. Record all three in mm and use the largest reading as your ring size โ fingers are at their largest after light activity.
C = d ร 3.14 and d = C รท 3.14. Memorise these two โ they let you instantly convert any diameter reading to circumference or vice versa without a chart, using just a phone calculator.