How to measure your ring size at home

Measure it now

Calibrate once with any bank card, then use whichever method you have to hand. Nothing is uploaded and nothing is stored except your screen’s scale, which stays in your browser.

Method 1 — a ring that already fits

This is the more accurate method, because a ring is a rigid object and a finger is not. Use a ring worn on the same finger of the same hand — hands differ, and so do fingers.

1. 1. Calibrate the screen. Hold any bank card upright against the screen and drag the slider until the outline matches its edges. Every card is 85.60 × 53.98 mm by ISO/IEC 7810, which is what turns pixels into millimetres. Keep browser zoom at 100%.
2. 2. Lay the ring on the circle. Adjust the circle until its outer edge touches the inside edge of your ring.
3. 3. Read every size at once. The result is inner diameter, and every national size computed from it.

The commonest mistake: measuring the outside of the band. You are measuring the space your finger occupies, not the metal around it. On a wide, thick band the difference is easily a full size.

Method 2 — a strip of paper

Use this when there is no ring to copy. You are measuring the circumference— the distance around the finger — and the tool converts it for you.

1. 1. Cut a strip about 1 cm wide. Narrower strips twist and read short; wider ones will not sit flat.
2. 2. Wrap it round the base of the finger. Snug and flat against the skin, with no slack and no pull. Mark where it overlaps.
3. 3. Check it passes the knuckle. Before unwrapping, slide the loop off over the knuckle. If it will not go, the ring will not either — widen it until it just passes, and use that.
4. 4. Flatten and measure to the mark, then set the tool above to Circumference and type the length in.

Why string gives the wrong answer

String, thread, dental floss and ribbon are all suggested constantly, and all share one problem: they stretch. Pulled taut round a finger, a length of string reads shorter than the finger actually is, and the error runs one way — always too small.

The arithmetic is unforgiving. One full US size is0.81 mm of diameter, which is only2.55 mm of circumference — about two and a half millimetres. Stretch a string by that much, which takes almost no force, and you have lost a whole size.

Paper does not stretch. If string is genuinely all you have, use it to mark the length and then measure the string flat against a ruler without tension — and treat the answer as approximate.

Measuring in centimetres or inches

Use whatever your ruler is marked in — the tool takes all three, and they are the same measurement written differently. Set the unit switcher above and type your number in.

One warning about inches. A quarter US size is0.2032 mm of diameter, which is about0.008 inches. An inch ruler marked in sixteenths cannot resolve that, and neither can a figure written to two decimal places. If you have a choice, measure in millimetres.

What your strip length means

Common paper-strip lengths and the sizes they come to. Every row is computed from the published standards, not copied from a chart. For anything between these, use the tool.

An em dash means that scale does not define a size there — it is not a gap in our data. Every system has a bottom and a top, and we would rather print nothing than invent a number.

If you cannot measure at all

Usually this means buying for someone else without asking. Ranked by how well they work:

• Borrow a ring they already wear. Measure it with method 1 and put it back. This is the only approach that is actually accurate. Note which finger it came from.
• Press one into soap or clay and measure the inner edge of the impression. Works, loses a little precision.
• Ask someone who would know — a sibling, a close friend. Less romantic, far more reliable than any guess.
• Fall back on the average.US 6 (16.51 mm) and US 9 (18.95 mm) are the commonly cited averages for women and men. This is a guess dressed as a number, and it is the reason engagement rings get resized so often — but if you must guess, guess here, and buy from somewhere that resizes.

Tracing round the outside of a finger with a pen does not work, and neither does comparing hand size. Both are widely repeated and neither survives contact with a ruler.

When to measure, and how tight is right

Fingers are not a fixed size. They swell in heat, after exercise, after salt, and late in the day; they shrink in cold. The swing across a single day is easily half a size, which is more than the difference the tool is resolving.

• Measure at the end of the day, at normal room temperature.
• Measure the same finger on the same hand you will wear the ring on.
• Measure two or three times on different days and take the largest.

A ring fits when it goes on with slight resistance, sits without pinching, and needs a small deliberate tug to come off. If it slides off freely it is too big — losing a ring is worse than a snug one. If your knuckle is much wider than the base of your finger, size to the knuckle: the ring has to get past it.