Ring Size Converter
UK, US, EU and Japanese sizes, from a measurement you can take with a strip of paper.
In short
Ring sizes are derived from the inside circumference of the band in millimetres. A US size 7 is about 54.4 millimetres, which is a UK N and an EU 54. Measure in the evening when fingers are largest, and measure the finger you will actually wear it on.
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Measuring at home
The paper strip method. Cut a strip of paper about 5 mm wide. Wrap it around the base of the finger, snug but not tight, and mark where it overlaps. Unwrap and measure to the mark in millimetres. That is your circumference.
From an existing ring. Measure the inside diameter across the widest point, in millimetres. This is more reliable if you have a ring that fits the right finger.
Circumference and diameter relate by pi, so a 54.4 mm circumference is a 17.3 mm diameter. Both are accepted above.
When to measure
Fingers change size through the day and with temperature, by up to half a size.
- Evening, at room temperature. This is close to your largest, which is what you want to fit.
- Not when cold. Fingers shrink noticeably, and a ring sized in winter can be tight in summer.
- Not straight after exercise or a salty meal, when hands are swollen.
- Measure the specific finger, on the specific hand. The dominant hand is usually slightly larger.
- Measure three times on different days and take the largest.
The three systems
| System | Based on | Notes |
|---|---|---|
| UK and Ireland | Letters A to Z with halves | Also used in Australia and New Zealand |
| US and Canada | Numbers, usually 3 to 13 | Half and quarter sizes are common |
| EU | Circumference in mm | The most logical: size 54 is 54 mm around |
| Japan | Its own numeric scale | Used across much of East Asia |
The EU system is the sensible one and worth using as your reference point, since it is simply the measurement rather than a coded version of it.
Band width changes the fit
A wide band sits against more of the finger and feels tighter than a narrow one of the same nominal size. For anything above about 6 mm wide, go up a quarter to a half size.
The same applies to comfort-fit bands, which are rounded on the inside. They generally slide on more easily, so some jewellers suggest going down a quarter size rather than up. Ask about the specific ring rather than applying a rule.
Buying as a surprise
The classic problem. A few approaches that work better than guessing:
- Borrow a ring they already wear on the correct finger and measure the inside diameter.
- Ask someone close to them who might already know.
- Buy slightly large. Resizing up is harder and more expensive than resizing down, and a ring that does not fit at all cannot be worn at the moment it matters.
- Check the resizing policy before buying. Many jewellers include one free resize, and some designs, particularly full eternity bands, cannot be resized at all.
Where home measurement is not enough
Paper stretches, and pulling it tight adds error in the direction of a ring that will not fit. For an expensive or sentimental purchase, get measured with a proper sizing gauge at a jeweller. It takes two minutes and costs nothing, and it removes the one variable you cannot correct afterwards.
Frequently asked questions
How do I measure my ring size at home?
Two ways. Wrap a strip of paper around the finger, mark where it overlaps, and measure the length in millimetres, which gives the circumference. Or measure the inside diameter of a ring that already fits, in millimetres, and enter that instead.
When should I measure?
In the evening, at normal room temperature. Fingers are smallest first thing in the morning and in the cold, and can swell by most of a size by the end of the day or in heat. Measuring at your largest avoids a ring you cannot get on in August.
How do UK and US ring sizes relate?
UK uses letters and US uses numbers, and the two do not map cleanly. A UK N is roughly a US 6.75, and each US whole size is about a UK letter and a half. EU sizes are simply the circumference in millimetres rounded, which is the most logical of the three.
Should I size up for a wide band?
Yes, usually by a quarter to a half size. A wide band covers more of the finger and feels tighter than a narrow one of the same nominal size. Anything above about 6 mm wide is worth allowing for.
How accurate is the paper strip method?
Good enough for a rough idea and not good enough for a surprise engagement ring. Paper stretches slightly and pulling it tight adds error. For anything expensive or irreversible, get measured properly with a sizing gauge at a jeweller.