How to measure your ring size at home, and read a US size

A ring is the one piece of jewellery where a guess is usually wrong. A necklace a few centimetres too long still works. A ring half a size too small can stick at the knuckle, and half a size too big can spin on the finger.

The fixed-size rings in this shop are listed in US sizes. Australian jewellers size rings by letter. This guide gets you from your finger to a US size, by way of millimetres, without a trip to a jeweller. Mazzucchelli's size guide notes that at-home methods are accurate for most rings, but that sizing in store is always best, especially for engagement rings and wider bands.

What a ring size actually measures

Every sizing system measures the same thing: the inside of the ring. The international standard, ISO 8653, defines ring size as the circumference of the largest cylinder that fits inside the ring. Mazzucchelli's guide says EU sizes use the inner circumference in millimetres, which is why they read as plain numbers like 52 or 54.

Australia and the UK use letters, and the US and Canada use numbers, as the same guide sets out. Letters and numbers are just labels for a circumference. Once you know yours in millimetres, you can read any chart.

Three ways to find your size

1. Measure a ring you already wear

This is the simplest method, because it starts from a ring you know fits. Use one that is worn on the same finger you are buying for; Mazzucchelli's advice is to always measure the exact finger the ring will go on. Lay the ring flat on a ruler and measure the inside diameter, straight across the middle, in millimetres. Don't include the metal. Then find the nearest diameter in the chart below.

2. Wrap a strip of paper around your finger

Cut a thin strip of paper, wrap it around the base of the finger, and mark where it overlaps. Unroll it and measure to the mark in millimetres. That is your finger's circumference, in the unit ISO ring sizes are based on. It is the same method Mazzucchelli describes.

Do it twice, and if the two readings land on different sizes, take the larger. Mazzucchelli's rule for anyone between sizes is to choose the larger or nearest half size, and our fixed-size rings come in whole sizes only. Check that the loop you measured would slide over your knuckle, because a ring has to get past it.

3. Skip the question with an adjustable ring

If you don't know your size, or you are buying for somebody else, an open band sidesteps the problem. Three of our adjustable rings are made that way:

• Sterling Silver Pearl Ring: genuine 925 sterling silver, a freshwater pearl, and an adjustable open band, with white, pink or purple pearl options.
• 925 Sterling Silver Ring with the cross design: an open band, sold in one size listed as Resizable.
• Gold Geometric Open Ring: an adjustable open band in 316L stainless steel with a gold-coloured finish, in five designs.

An open band has a gap that opens or closes a little to change the fit. The product pages don't give adjusting instructions, so if you are unsure, message us before bending it.

When to measure

Fingers change size through the day. Mazzucchelli's advice is to measure in the afternoon or at the end of the day, when your hands are warm. A ring sized on a cold morning can feel tight by evening.

Knuckles matter too. By the same guide, a ring should pass over the knuckle with slight resistance and then sit comfortably without spinning. If your knuckle is noticeably wider than the base of your finger, size for a ring that gets past it with that slight resistance. A ring that won't go on is no use at all.

Band width changes the fit as well. Mazzucchelli says wide bands, 5mm and over, usually fit tighter, and suggests going up half a size. Lily Dia's chart gives the same advice for bands wider than 3mm. If going up half a size puts you between two of our whole sizes, choose the larger.

US to Australian ring sizes

These are the US sizes our fixed-size rings come in, with the Australian letter and measurements from Mazzucchelli's chart:

Charts don't all agree on the letters. Mazzucchelli puts a US 6 at L, while Lily Dia's chart puts it at L½, and the same half-letter gap runs through every whole size from US 5 up. Their millimetres agree to within a tenth of a millimetre. That is the reason to work in millimetres: measure, find your diameter or circumference, and read the US size from that row. If you already know your Australian letter from a jeweller, treat the conversion as approximate and check it against a measurement.

Three rings and their sizes

• Moissanite Solitaire Ring: US 5 to 9, a six-prong solitaire in solid 925 sterling silver.
• Zircon Stone Ring: US 5 to 10, a round stone set in 925 sterling silver.
• Micro Pave Zircon Ring: US 5 to 10, in rose gold, gold or silver colour, with a slim profile meant for stacking.

None of these pages gives a band width. If you plan to stack the Micro Pave Zircon Ring with another ring on the same finger, here is our own suggestion, which the sizing guides don't cover: two rings can feel snugger than one, so if you are between two sizes, choose the larger.

If it doesn't fit

You can ask to return a ring within 14 days of delivery. It has to be unworn, with tags still on, in the original packaging, with your receipt or proof of purchase, and sale items can't be returned. Message us first, before posting anything, and return postage is yours to pay. A ring worn around to see whether it loosens up is no longer unworn, which is the practical reason to measure first.

If we sent the wrong size or the ring arrives faulty, message us straight away with a photograph and you won't pay to send it back. Otherwise, the quickest route to a different size is to return the one you have and order the right one separately, rather than waiting on an exchange. The rings collection has every ring in one place, fixed and adjustable.