How to Find Out Someone’s Ring Size Without Asking
Borrow a ring they wear on the same finger and hand, then measure its inside or trace it. If neither is possible, ask a friend or relative who knows, or choose a ring that can be adjusted.
Borrow a Ring They Wear
If you can, borrow a ring they wear on the same finger and hand as the ring you plan to give. Which finger matters: a ring worn on a different finger or hand can be a different size.
Put the ring back where it was after measuring. Use the on-screen ring sizer, print the circle sizer and compare the ring’s inside edge, or measure its inside diameter in millimetres. A ring with an inside diameter of 17.3 mm is US 7, UK N½, ISO 54.
Make an Imprint or Trace
If you cannot keep the ring long enough to measure it, press it into a bar of soap or onto a sheet of paper. You can also draw around the inside edge.
Measure the imprint or tracing later with the on-screen sizer, printed circles, or by checking the inside diameter. Keep the mark clear and avoid pressing hard enough to damage anything.
Compare with a Ring You Know
You can try their ring on your own finger and compare it with a ring you know fits you. This gives a rough clue, since your fingers may differ in size.
Do not treat the comparison as a measurement. A ring that feels similar on your hand may not fit the same way on theirs.
Ask Someone Who Knows
A friend, sibling or parent may already know their ring size, or may be able to suggest a discreet way to check.
A jeweller can work from an inside diameter in millimetres or from a tracing, so write down what you measure.
If You Cannot Find Out
Some rings can be resized and some cannot. Ask about resizing before you buy, including whether the ring style can be adjusted.
A half US size is 0.4 mm of inside diameter, so a small miss is a small difference. Check the jeweller’s resizing options before choosing.