Free calculator
Ring Size Converter
Wrap a strip of paper around the base of your finger, mark where it overlaps and measure the length in millimetres. Do it in the evening when fingers are warm, and repeat three times.
How it works
ISO/EU size is the inside circumference in millimetres. US size = (inside diameter − 11.63 mm) ÷ 0.8128 mm. UK letter sizes step by about 1.27 mm of circumference per letter.
Indian jewellers use more than one numbering system, so give your circumference or diameter in mm when you order.
Frequently asked questions
Wide bands fit tighter. What do I do?
For bands wider than 6 mm, go up by roughly a quarter to half a US size.
Which finger should I measure?
The finger you will wear it on, at the base, not at the knuckle.
Do ring sizes change?
Yes, with temperature, salt intake, time of day and pregnancy. Aim for a ring that slides over the knuckle with slight resistance.
General estimates for information only. Not medical or professional advice. Nothing you enter is saved or sent to us.
