Circumference is the distance around your finger, and it is the measurement European sizing is built from. Here is how to take it properly.
Enter your circumference reading in the first field.
Your size
This page walks through one method in detail: measuring the finger itself. For a complete overview, see how to measure ring size at home.
Circumference is the distance around your finger. It is the measurement you get by wrapping something round the finger and reading where it overlaps, and it is the most direct thing you can measure when you have no ring to work from.
It is also the measurement that European sizing is built on. An EU size 54 ring has a 54 mm inside circumference — the size and the measurement are the same number. That makes circumference the most useful single figure to know.
A strip of ordinary paper about 5 mm wide and 100 mm long, a pen, and a ruler with millimetre markings. That is genuinely all.
Use paper rather than string. Paper does not stretch, and stretch is the single largest source of error in this method. The case against string in detail.
Enter the number into the calculator at the top of this page, or read it off the chart below. Because circumference is a physical measurement rather than a regional label, one reading gives you every system at once.
| Inside circumference | US / Canada | UK / AU / IE | EU / ISO |
|---|---|---|---|
| 49.3 mm | 5 | J½ | 49 |
| 50.6 mm | 5.5 | K½ | 50–51 |
| 51.9 mm | 6 | L½ | 52 |
| 53.1 mm | 6.5 | M½ | 53 |
| 54.4 mm | 7 | N½ | 54 |
| 55.7 mm | 7.5 | O½ | 56 |
| 57.0 mm | 8 | P½ | 57 |
| 58.2 mm | 8.5 | Q½ | 58 |
| 59.5 mm | 9 | R½ | 59–60 |
| 60.8 mm | 9.5 | S½ | 61 |
| 62.1 mm | 10 | T½ | 62 |
Circumference and inside diameter describe the same ring. Circumference is diameter multiplied by pi (roughly 3.1416), so:
Circumference = diameter × 3.1416
Diameter = circumference ÷ 3.1416
A US 7 has a 17.3 mm inside diameter, which is 17.3 × 3.1416 = 54.4 mm of circumference. If a retailer lists only one of the two, you can always work out the other.
The most common error, and it always pushes in the same direction — too small. Skin compresses. If the strip is denting the finger, you are measuring your finger under load rather than at rest, and the resulting ring will feel tight from the first day.
A finger measured at 7am and the same finger measured at 6pm can differ by around half a size, and more in hot weather or after salty food. When to measure and why fingers change.
Fingers on the left and right hand differ, commonly by around half a size, and for most people the dominant hand is slightly larger. Measure the exact finger that will wear the ring.
Your circumference reading describes your finger, not the ring. A band 6 mm wide or more covers more of the finger and wears tighter than a slim band at the same nominal size. How much to add for band width.
Enough to matter. A half size is only about 1.25 mm of circumference, and strip tension, temperature and time of day each move a reading by a comparable amount. Take several readings rather than trusting one, and for anything expensive have a jeweller confirm the size on a metal sizer before you order.
Snug enough to stay put, loose enough that it is not denting your skin. If you can see flesh bulging on either side of the strip you are pulling too hard, which typically costs you around half a size. You should be able to rotate the strip slightly around the finger.
The most commonly ordered women's sizes correspond to roughly 51.9 to 54.4 mm of circumference (US 6 to US 7). For men it is roughly 59.5 to 62.1 mm (US 9 to US 10). These are the busiest part of the distribution rather than a reliable guess for any individual.
Yes, provided it is a soft flat tape marked in millimetres and you can read it accurately at that scale. Do not use a retractable metal tape — the blade is curved and springy, so it will not lie flat against the finger and will read too large.
Measure both and use the larger. The base tells you how the ring will sit day to day, but the knuckle determines whether the ring can get on and off at all. If the knuckle reading is bigger, that is your constraint.
Most jewellers suggest the larger of the two, because a slightly loose ring can be sized down while a ring that will not clear your knuckle cannot be worn at all. The full decision, including when to size down instead.
If you own a ring that fits, measuring it is more accurate than measuring your finger.
Circumference and EU sizesEU sizes are circumference in millimetres, so your reading is already an EU size.
Errors that skew a measurementWhat each common mistake costs you, in millimetres.
When to take the readingTiming changes the result by about half a size across a normal day.