How to Find Her Ring Size for a Surprise Proposal

Buying an engagement ring in secret means sizing without asking. These methods, roughly in order of reliability, will get you close enough that a small adjustment afterwards is all that is needed.

1. Borrow an existing ring

The best option by far. Take a ring she already wears on the correct finger — usually the fourth finger of the left hand in the UK, US and much of Europe — and either measure the inside diameter with a ruler, or take it to a jeweller who will size it in seconds. Return it before it is missed.

2. Press a ring into soap or clay

If the ring cannot leave the house, press it flat into a bar of soap, modelling clay or a stick of lip balm to leave a clean impression. Measure the diameter of the impression, or photograph it beside a ruler.

3. Trace the inside outline

Place the ring on paper and draw carefully around the inside edge with a sharp pencil. Measure across the circle. This is less precise than a physical impression but usually lands within half a size.

4. Ask someone who knows

A sibling, best friend or parent may already know, or can find out casually. Enlist one accomplice, not three; the more people involved, the more likely the surprise unravels.

5. Compare with your own hand

If she has ever tried on one of your rings, note where it sat. A ring that reached the second knuckle of your little finger gives a rough starting point. Treat this as a last resort.

6. Buy the average and resize later

The most common women's engagement ring size in the UK and US is around a US 6 to 6½, or UK L½ to M½. If you have no information at all, this is a reasonable gamble, and most jewellers include one free resize with an engagement ring purchase.

Protecting yourself

Before you buy, confirm three things with the retailer: is the ring resizable, is the first resize free, and what is the returns window. Full eternity bands and some tension or bezel settings cannot be resized at all, which turns a guess into an expensive problem.

If it is wrong on the night

It does not matter. A ring that is slightly loose can be worn carefully for a few days, and one that is too small can be worn on another finger for the photographs. Resizing takes most jewellers a week and costs relatively little, and the story of the ring that had to be resized becomes part of the memory rather than a disaster.

Use the converter to record the measurement you obtain in millimetres so it stays accurate whichever country you buy in.