You can measure a ring size at home accurately enough to buy with confidence, as long as you use the right method and measure more than once. The two that work are measuring the circumference of the finger with a strip of paper, and measuring the inside diameter of a ring the person already wears.

The methods that do not work reliably are the string trick and printed paper ring sizers, and it is worth knowing why before you rely on either.

Method 1: measure the finger with a paper strip

This is the best home method when you can measure the actual finger.

1. Cut a strip of ordinary printer paper about 5mm wide and 10cm long. Paper, not string.
2. Wrap it snugly around the base of the correct finger — snug enough that it will not slide off, not tight enough to pinch.
3. Mark where the end of the strip overlaps, with a fine pen or a pencil.
4. Check it will pass over the knuckle before you unwrap it. Slide the loop up and off. If it will not go over the knuckle, that is your real limit and you need to measure the knuckle instead.
5. Unwrap and measure from the end of the strip to the mark, in millimetres, with a ruler.

That measurement is the circumference. Look it up in the chart below.

Do it three times on three different days, in the late afternoon, at normal room temperature. Take the reading that comes up most often.

Method 2: measure a ring they already wear

Use this when you are buying a surprise, or when the person is not with you.

1. Borrow a ring that they currently wear on the correct finger of the correct hand.
2. Lay it flat and measure straight across the inside of the band, from the inner edge on one side to the inner edge on the other, through the centre. That is the internal diameter.
3. Measure in millimetres. A digital caliper is ideal. A steel ruler works if you are careful.
4. Look the diameter up in the chart.

The common mistakes here are measuring the outside of the band rather than the inside, and measuring off-centre. Both make the ring come out too large.

You can also press the ring into a bar of soap or a piece of plasticine to leave a clean impression and take the ring back before anyone notices, then measure the impression.

UK ring size chart

UK sizes use letters. Measure either the circumference of the finger or the inside diameter of an existing ring, then read across.

UK size	Inside diameter (mm)	Circumference (mm)	US size
H	14.9	46.8	3.75
I	15.3	48.0	4.25
J	15.7	49.3	4.75
K	16.1	50.6	5.25
L	16.5	51.8	5.75
M	16.9	53.1	6.25
N	17.3	54.4	6.75
O	17.7	55.7	7.25
P	18.1	57.0	7.75
Q	18.5	58.3	8.25
R	18.9	59.5	8.75
S	19.4	60.8	9.25
T	19.8	62.1	9.75
U	20.2	63.4	10.25
V	20.6	64.6	10.75
W	21.0	65.9	11.25
X	21.4	67.2	11.75
Y	21.8	68.5	12.25
Z	22.2	69.7	12.75

If your measurement falls between two sizes, go up rather than down — a fraction loose can be corrected, a ring that will not pass the knuckle cannot be worn at all while you wait for it to be altered.

Two methods to avoid

String or cotton thread. String stretches. Even a small amount of stretch changes the reading by a full size, and it also compresses into the skin more than paper does. It is the most common cause of a home measurement coming out too small.

Printed paper ring sizers. These only work if the page prints at exactly 100% scale, and most printers quietly scale to fit the margins. If you do use one, print it, then check the printed scale bar with a ruler before trusting anything on the page.

Measure at the right moment

Fingers change size through the day, and this is the biggest source of error after using string.

• Late afternoon or early evening is closest to your average size. First thing in the morning is your smallest.
• Normal room temperature. Cold hands can read a full size down.
• Not straight after exercise, a salty meal, alcohol or a hot bath — all of these swell the fingers.
• Correct hand. The dominant hand is usually a quarter to a half size larger.

Measure across three separate days and take the most common result. A single reading is a guess; three matching readings is a size.

Buying a surprise ring: how to guess well

If you genuinely cannot get a measurement, here is how to narrow it down honestly.

• Borrow a ring from their jewellery box — but only one they wear on the ring finger. A ring worn on the middle or index finger will be one to two sizes larger.
• Ask a close friend or family member with similar hands to try rings on and report their own size.
• Slide one of their rings onto your own finger and mark where it stops with a pen, then have a jeweller measure your finger at that mark.
• If all else fails, buy the design and get it sized after the proposal. A plain or half eternity band can normally be resized; the fitting is a routine job.

Common UK sizes are a useful last resort, though they are a rough guide only: many women’s ring fingers fall around L to O, and many men’s around Q to V. Plenty of people sit outside those ranges.

Band width and design change the size you need

A wide band grips more of the finger than a narrow one, so it feels tighter at the same nominal size. A rule of thumb in the trade, not a measured figure: for a band 6mm or wider, allow about a quarter to a half size extra.

Design also decides whether a mistake is fixable. Plain and half eternity bands can normally be resized. Full eternity bands, where stones run right round the ring, cannot be — they have to be remade at the correct size.

So if you are measuring at home and want a safety margin, start with something adjustable. A stackable baguette cut half eternity band or a twisted round cut half eternity band both leave plain metal on the underside for a jeweller to work with. If you want a clean, easy first ring to size, a minimalist round cut wedding band is the most forgiving of all.

Frequently asked questions

How accurate is home measuring, really?

With a paper strip, measured three times in the late afternoon, most people land within half a size. That is close enough to buy a resizable band. It is not close enough to commit to a full eternity ring.

Can I use a ruler to measure an existing ring?

Yes, but measure the inside diameter through the centre, not the outside, and use a ruler with clear millimetre markings. A digital caliper is far more accurate and inexpensive.

What if the measurement falls between two sizes?

Round up. A slightly large ring can be brought in with sizing beads or a resize. A ring that will not pass the knuckle is unwearable until it is altered.

Does the knuckle matter more than the base of the finger?

If your knuckle is wider than the base of the finger, yes — the ring must clear the knuckle. Size to the knuckle, then have small sizing beads fitted inside so the ring does not spin once it is on.

Is a UK size the same as a US size?

No. UK sizes are letters, US sizes are numbers, and they do not line up neatly. Use the chart above, and always state which system you are quoting when you order.

Before you order

Measure with paper, in the afternoon, on the right hand, three times. Round up if you are between sizes. Pick a resizable design if you are buying a surprise.

All our bands are hand-made in solid gold and platinum with lab-grown diamonds, and every order includes free insured UK delivery and 30-day returns, so getting the size sorted is straightforward. Have a look at the wedding ring collection or the engagement rings when you are ready.