UK Bra Size Calculator

How the calculator works

The calculator does two small sums. Your band is your underbust measurement rounded to the nearest even number. Your cup is the difference between your bust measurement and that band, at one cup letter for every inch. The same figures are set out as a grid in the UK bra size chart.

Nothing is added to your underbust. If you have used a size guide that told you to add four or five inches, you will probably get a smaller band and a bigger cup letter here. That is expected, and the reasons are worth a few minutes if the result surprises you.

Worked examples

Underbust 32 in, bust 37 in

The underbust is already an even number, so the band is 32. The bust is 5 inches bigger than the band, and 5 inches is a DD. Starting size: 32DD.

Underbust 29 in, bust 35½ in

Twenty-nine sits exactly between a 28 and a 30. On a 30 band the difference rounds to 6 inches, which is an E, so the calculator suggests 30E and offers 28F as the firmer alternative. Both hold the same volume. The right one is whichever band feels secure without being painful.

Underbust 81 cm, bust 99 cm

Eighty-one centimetres is 31.9 inches, which rounds to a 32 band. Ninety-nine centimetres is 39 inches, 7 more than the band, which is an F. Starting size: 32F, labelled 70G in most European sizing.

Getting measurements you can trust

• Underbust: tape directly under the breasts, level all the way round, pulled snug. Breathe out normally and read the number.
• Bust: tape around the fullest part, resting on the skin without pressing in. If your breasts are soft or sit low without a bra, lean forward to 90 degrees and measure there as well. A much bigger leaning figure means the standing one is underestimating you.
• Take each one twice. A tape that has slipped down at the back can add an inch, and an inch is a whole cup size.

No tape measure? See how to measure without one. Prefer metric throughout? Use the cm calculator. The full technique, with the mistakes that most often throw results off, is in how to measure your bra size.

Reading your result

Your starting size

This is the first size to pull off the rail. It is the best estimate two measurements can give, and it is right or within one size for most people.

Sister sizes

These are the neighbouring sizes with the same cup volume: one band down with one cup up, and one band up with one cup down. They help when the cups feel right but the band does not, or when your size is out of stock. The sister size chart shows the full pattern.

International labels

US bands match UK bands, but the cup letters part ways after DD. European and French sizes use centimetre-based bands and a plain alphabet for cups. If a bra's label does not say which system it uses, check before you order. The international chart has every conversion.

What a calculator cannot tell you

Two people can share the same two measurements and need different bras. A tape measure records circumference. It cannot record how your breast tissue is distributed, how wide or narrow it sits on your chest, or how firm it is. Brands add their own variation on top, because there is no enforced UK sizing standard.

So the result is where you start. The test that matters is how the bra behaves on your body: a level band, cups that contain everything without gaps, wires that sit flat on your ribs. If something is off, match the symptom to its cause and adjust by one size at a time. We set out the limits in more detail in how accurate bra size calculators are.

Sports, maternity and nursing bras

Your everyday size is the basis for these, with adjustments. The sports bra calculator adds support type and impact level, and converts to S, M, L sizing where that applies. The nursing bra calculator allows for the changes at each stage of pregnancy and feeding.

Frequently asked questions

Should I measure with a bra on?

Measure your underbust on bare skin. For the bust, go braless or wear a thin, unpadded, non-minimising bra. Padding adds to the bust figure and a compressive bra reduces it, and either one moves the cup result.

My underbust is an odd number. Which band do I pick?

An odd number sits between two bands. The calculator shows both options as a pair of sister sizes with the same cup volume. Most people start with the firmer band if they have soft tissue around the ribs, and the looser one if their ribcage is bony or they dislike a firm fit. Try both if you can.

Can I enter centimetres?

Yes. Switch the unit to centimetres and type what the tape shows. The calculator converts to inches internally because UK band sizes are based on inches, then gives you a UK size plus the EU and French labels, which are centimetre-based.

Why is the cup bigger than I expected?

Because the band is probably smaller than the one you usually wear. Cup letters are relative to the band, so when the band comes down the letter goes up to keep the same volume. A 36C and a 32DD hold the same amount. A bigger letter on a smaller band does not mean a bigger bust.

Does this work for sports or nursing bras?

It gives the everyday size those are based on. Sports bras add questions about compression and impact level, and pregnancy and feeding change your measurements from month to month, so each has its own calculator on this site.