Ring size 8 in mm
Type a measurement and the sizes appear here.
Sizes are for guidance, following BS 6820 and ISO 8653 as checked on 2026-10-23. Brands cut sizes differently: try the ring on or ask your jeweller before you buy. Disclaimer
US ring size 8 has an inside diameter of 18.1 mm and an inside circumference of 57.0 mm. Jewellers cut to the circumference, so 57.0 mm is the number to quote when you order.
Size 8 in every sizing system
| System | Size |
|---|---|
| United States, Canada and Mexico | 8 |
| UK, Ireland, Australia, New Zealand, South Africa | P½ |
| Europe (ISO 8653) | 57 |
| Japan (号, JCS) | 16号 |
| China and Hong Kong (港号) | 18 |
| India | 17 |
| Italy, Spain and Switzerland | 17.0 |
| Inside diameter (mm) | 18.1 mm |
| Inside circumference (mm) | 57.0 mm |
The sizes on either side
A half size is only about 1.3 mm of circumference — thinner than a matchstick. If your own measurement lands between two rows, take the larger one: a ring that is slightly loose can be made smaller, and it will still go on over a swollen summer knuckle.
| US | Diameter | Circumference | UK / AU | EU / ISO | JP 号 |
|---|---|---|---|---|---|
| 7 | 17.3 mm | 54.4 mm | N½ | 54 | 14号 |
| 7½ | 17.7 mm | 55.7 mm | O½ | 56 | 15号 |
| 8 ◀ | 18.1 mm | 57.0 mm | P½ | 57 | 16号 |
| 8½ | 18.5 mm | 58.3 mm | Q½ | 58 | 18号 |
| 9 | 18.9 mm | 59.5 mm | R½ | 60 | 19号 |
Who wears this size
This sits inside the range jewellers keep in stock for men, so it is usually available off the shelf and quick to order.
Check that this really is your size
Before you order, measure rather than assume. The quickest check is a strip of paper round the finger: wrap, mark the overlap, measure the length in millimetres and compare it with the circumference above.
If you already own a ring that fits the right finger, match it to a circle on the screen or print the circle chart and lay the ring on it. Measure the inside of the band — on a wide ring the outside is more than a size larger.
Wide bands fit tighter. From 4 mm wide add a quarter size, from 6 mm add a half.
Questions people ask
What is ring size 8 in mm?
US ring size 8 is 18.1 mm across the inside of the band and 57.0 mm all the way round the inside.
What is US ring size 8 in UK sizes?
It is UK P½. British charts from different jewellers can be half a size apart — this one follows BS 6820:1987, where one letter is 1.25 mm of circumference — so check the chart of the shop you are buying from.
What is US ring size 8 in EU sizes?
EU/ISO 57. ISO 8653 sizes are simply the inside circumference in millimetres, and size 8 measures 57.0 mm round.
What is US ring size 8 in Japanese 号?
Closest to 16号. The exact figure is 16.4号, and Japanese sizes come in whole numbers only, so the two scales never line up perfectly.