How to get the ring size

How UK ring sizing works

UK ring sizes use letters of the alphabet, running from A (very small) to Z, with half sizes available (for example, M½ or N½) ⁽¹⁾. Each letter represents a specific inner circumference measured in millimetres – roughly 1.25mm of circumference between each letter step ⁽²⁾. This is different from the US system (which uses numbers) and the EU system (which uses millimetres directly), so if you are reading sizing guides online, always check they are written for the UK market.

Average UK ring sizes

These are starting points only – individual fingers vary considerably:

Average UK size

Approximate circumference

Women

L–M

50–52mm

Men

T

around 61mm

If you are buying a ring as a surprise and have no other information to go on, size M or N for a woman is a reasonable starting estimate ⁽³⁾.

Four ways to find your partner's size secretly

1. Borrow an existing ring

This is the most accurate method. If your partner wears a ring on their left ring finger – the finger where an engagement ring traditionally sits in the UK – borrow it when they are unlikely to notice ⁽⁴⁾. Take it to a jeweller, who will measure it in minutes, often for free. If visiting a jeweller is not convenient, place the ring on white paper, trace the inner circle carefully, and measure the diameter across the traced circle. Compare this to a UK ring size chart.

Key tip: Use a ring they wear regularly on the correct finger. A ring worn on a different finger, or one that has not been worn for a long time, may not be an accurate guide to their current everyday size ⁽⁴⁾.

2. Ask a trusted friend or family member

A close friend, sibling, or parent of your partner can find out the size naturally, without arousing suspicion. Approaches that work well:

• A recently engaged friend can offer to let your partner try on their engagement ring under the guise of admiring it ⁽⁵⁾
• A family member can bring up jewellery in conversation and ask directly what size your partner is
• A friend can take your partner to browse rings as a casual outing, noting which sizes fit ⁽⁵⁾

3. Try the ring on yourself

Slip one of your partner's existing rings onto your own finger and note where it stops. You can then either take that measurement to a jeweller, or use an inexpensive ring sizer (available online for a few pounds) to measure that point on your own finger ⁽⁶⁾. This is less precise than having the ring professionally measured but works well as a quick approximation.

4. The string method – use as a last resort

Wrap a thin strip of paper or thread gently around the base of your partner's ring finger while they are asleep, mark where it overlaps, and measure the length in millimetres. This is the circumference of the finger, which can be converted to a UK letter using a sizing chart ⁽⁷⁾. This method works but carries obvious risks – a light sleeper makes it impractical.

What affects ring size

Even with an accurate measurement, it is worth knowing that ring size is not entirely fixed:

• Fingers are slightly larger in the evening and in warm weather, and slightly smaller in the cold ⁽⁸⁾
• A wider band covers more of the finger and feels tighter at the same letter size – if the ring has a wide band (6mm or more), consider going up half a size ⁽²⁾
• Fingers can change size over time due to weight changes, pregnancy, or age

What if the size is wrong?

Do not worry too much. Most engagement rings in gold or platinum can be resized by up to two sizes, and many UK jewellers include a complimentary first resize ⁽³⁾. It is worth asking about this before you commission – some jewellers offer free resizing within a set period after delivery.

A few settings and design styles are more difficult to resize, including:

• Full eternity bands with stones all the way around
• Rings with very intricate patterning along the full shank
• Rings made in materials that cannot be cut and rejoined, such as tungsten or ceramic

If the design you want falls into one of these categories, getting as accurate a size as possible before making becomes more important.

When in doubt: propose first, choose together

If finding the size secretly is genuinely not possible, many couples choose to propose with a placeholder ring or a simple solitaire, then visit a jeweller together to design or select the actual engagement ring afterwards ⁽⁹⁾. This is increasingly common and removes all sizing uncertainty, while still making the proposal itself a complete surprise.