Ring Size Calculator
Convert a finger measurement into a ring size in any of the four main systems. Measure either the circumference or the diameter — the calculator handles both.
Find Your Ring Size
Measure your finger and convert to any ring size system
Your ring size
6.1
Updates as you type — nothing is sent anywhere.
How to measure your finger
For circumference, wrap a strip of paper or a length of string around the base of the finger, mark where it overlaps, and measure the length in millimetres against a ruler. For diameter, take a ring that already fits that finger and measure straight across the inside opening. Circumference is the more reliable of the two, because a small error in diameter is multiplied by roughly three.
What each system counts
US sizes run on a numeric scale where each full size adds about 2.55 mm of circumference. EU sizes are the circumference in millimetres, near enough directly. Japanese sizes use their own numbered scale offset from the circumference, and Indian sizes track closely to the UK alphabetical scale expressed as numbers.
Measure at the right moment
Fingers change size through the day and with temperature — they are smallest in the cold morning and largest in heat or after exercise. Measure in the evening at normal room temperature for a size that will be comfortable most of the time. If your knuckle is noticeably wider than the base of the finger, size so the ring passes the knuckle, then consider having it fitted with sizing beads.
Band width changes the fit
A wide band sits on more of the finger and feels tighter than a narrow one at the same nominal size. For bands over about 6 mm wide it is common to go up a half size. Comfort-fit bands, which are domed on the inside, usually run large — often a half size down from your measured size.
Frequently asked questions
Can I measure my ring size with string?
Yes. Wrap string or a paper strip snugly around the base of the finger, mark the overlap, and measure that length in millimetres. Enter it as the circumference.
What is a 52 mm ring size in US?
A 52 mm circumference is approximately a US size 6. Select 'Circumference', enter 52, and set the output to US.
Should I size up for a wide band?
Usually yes. Bands wider than about 6 mm contact more of the finger and feel tighter, so a half size up is a common adjustment.
When is the best time to measure?
In the evening, at normal room temperature. Fingers are at their smallest when cold and swell in heat, so a morning measurement can give a ring that is uncomfortable later.