How to measure your ring size at home

Method 1: measure a ring that already fits

This is the method GIA describes as a good way to size at home: use a ring that fits the finger you’re buying for, and measure or trace its inside (GIA).

1. Pick a ring that fits the same finger on the same hand. Fingers on each hand can differ.
2. Measure straight across the inside of the ring, edge to edge, in millimetres. Don’t include the metal.
3. Look up that inside diameter in our ring size chart. It shows the US, UK, European and Japanese size.

A ruler marked in millimetres works. If you don’t have one, our online ruler shows real millimetres once you set it with a bank card.

Method 2: use a printed ring sizer

Our ring size chart page has a printable sizer: circles at real size for each size, plus a 50 mm check bar.

1. Print at 100% (“Actual size”), never “Fit to page”.
2. Measure the 50 mm bar with a real ruler. If it isn’t exactly 50 mm, the circles are the wrong size and the sheet is no use.
3. Lay a ring that fits on the circles. Your size is the circle that matches the ring’s inside edge.

Method 3: string or paper strip (least reliable)

You can wrap a strip of paper around your finger, mark where it meets, and measure the length. That length is the circumference. GIA warns that string and paper methods lead to inaccuracies (GIA), so treat the result as a rough guide only.

How sizes are numbered

• US and Canada: numbers, in half sizes (for example 6, 6½, 7).
• UK and Australia: letters, with half sizes (for example M, N, O).
• Europe: the inside circumference in millimetres. The 1986 edition of the international standard, ISO 8653, defined ring size this way (ISO); the current edition is ISO 8653:2016 (ISO).
• Japan: numbers. In our chart they go up by one for each extra millimetre around, the same way The Measure App works them out.

Charts from different jewellers can differ by a fraction of a size. If you’re buying online, use the seller’s own chart if they have one.

Before you buy, see a jeweller

Home sizing is a good starting point, not the final answer. GIA’s advice is to ask a jeweller to measure ring size, because they can allow for things like temperature and time of day: fingers shrink in the cold and swell in the heat (GIA). Jewelers of America also recommends having your fingers professionally sized (Jewelers of America).

Sizing a ring with your iPhone

The Ring Size tool in The Measure App works like Method 1 without the ruler: place a ring on the circle on your screen, slide until the circle touches the ring’s inside edge, and read the size in four systems. The app draws the circle at real size for each iPhone and iPad model. The result is still approximate, and the app says so: ask a jeweller to check the size before you buy.