Bra Size Calculator UK

Shopping for bras in Britain means navigating one of the quirkiest sizing languages in the world — a ladder of double letters like DD, FF and GG that the American system never uses. This free UK bra size calculator estimates your UK bra size from two tape measurements: your underbust and your bust. The whole thing takes under a minute, works in inches or centimetres, and speaks fluent UK sizing from AA all the way to J.

The maths is simple. Pop in your underbust — taken firmly just beneath your bust — and your bust — taken round the fullest point. Your underbust rounds to the nearest even inch to give your band size, and the gap between bust and band sets your UK cup: about an inch of difference per letter, climbing the UK ladder of AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH and J. Try Simple mode for the quick two-measurement answer, or Advanced mode with six measurements for a more considered estimate.

One honest warning before you start: the number on the label is a starting point, not a promise. UK brands all cut a little differently, and the same letters can fit differently from one label to the next. Treat your result as the first size to try — then trust the mirror and how it feels.

Enter Your Measurements

Not sure how to measure? See how to measure your bra size.

How to Measure for a UK Bra Size

All you need is a soft tape measure and a couple of minutes. Wear a thin, unpadded bra — or none — so the tape rests against your body, and check in a mirror that the tape stays level.

  1. Underbust first. Wrap the tape firmly around your ribcage, right where a bra band would sit, keeping it horizontal. Breathe out normally and note the measurement.
  2. Then the bust. Wrap the tape round the fullest part of your bust, level all the way round and firm without digging in. Note that number too.
  3. Enter both above — in inches or centimetres — and hit Calculate. The calculator does the rest, working in the UK cup-letter system.

Want the detailed walkthrough with tips for each measurement? See how to measure your bra size.

UK Bra Size Chart

This chart shows common UK bra sizes by band and cup. Bands are in inches and always even numbers; cups follow the UK letter progression with its characteristic double letters. Scroll sideways on smaller screens.

BandABCDDDEFFFGGGHHHJ
2828A28B28C28D28DD28E28F28FF28G28GG28H28HH28J
3030A30B30C30D30DD30E30F30FF30G30GG30H30HH30J
3232A32B32C32D32DD32E32F32FF32G32GG32H32HH32J
3434A34B34C34D34DD34E34F34FF34G34GG34H34HH34J
3636A36B36C36D36DD36E36F36FF36G36GG36H36HH36J
3838A38B38C38D38DD38E38F38FF38G38GG38H38HH38J
4040A40B40C40D40DD40E40F40FF40G40GG40H40HH40J
4242A42B42C42D42DD42E42F42FF42G42GG42H42HH42J
4444A44B44C44D44DD44E44F44FF44G44GG44H44HH44J

AA cups also exist in UK sizing. Note there is no single I in the standard UK progression — the ladder runs H, HH, then J.

How UK Cup Sizing Works

UK sizing pairs an inch-based band number with a cup letter — and it is the cup letters that make the UK system distinctive.

The UK cup ladder

From the smallest, the UK cup progression is AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J. Each step up the ladder represents roughly one more inch of difference between your bust and band measurements. Notice the doubled letters: after F comes FF, after G comes GG, and after H comes HH — a convention the US system simply doesn't share.

There is no DDD in UK sizing

This is the single most important thing to know when switching between systems. Where the US puts DDD after DD, the UK puts E. They represent roughly the same cup volume, but the letters are not interchangeable — a label reading DDD is using US (or US-style) sizing, not UK.

A UK F is not a US F

Because the two ladders diverge after DD, letters that look identical can mean different volumes. A UK F is the 7th cup step (after E); US brands rarely use a single F at all in that range, typically labelling the equivalent volume G. Never assume a matching letter means a matching fit across systems — check which system the brand follows.

A worked example

Say your underbust measures 33 inches and your bust measures 37 inches. The band rounds to 34. The 3-inch difference lands on C in the UK progression. Your estimated UK size is 34C — the same letters you'd get in the US at this point on the ladder, since the systems only split above DD.

US vs UK Bra Sizes Compared

Band numbers are the same in both systems — the split is entirely in the cup letters. This table lines up the two ladders by bust-minus-band difference so you can see exactly where they part ways:

Bust − band differenceUS cupUK cupLetters match?
1 inchAAYes
2 inchesBBYes
3 inchesCCYes
4 inchesDDYes
5 inchesDDDDYes
6 inchesDDDENo — different letters
7 inchesGFNo — different letters
8 inchesHFFNo — different letters
9 inchesIGNo — different letters
10 inchesJGGNo — different letters

A few cautions. These pairings line up cups of the same nominal volume — they are approximations, not exact equivalents, because brands in each country grade their patterns independently. Some US brands also use F where DDD would be, and a few UK labels skip letters or extend the ladder differently. When in doubt, shop by the system the brand actually uses: our US bra size calculator covers the American ladder, and the US, UK and EU size guide compares all three systems.

UK Sister Sizes

Sister sizes keep roughly the same cup volume while changing the band: go down a band and up a cup, or up a band and down a cup. In UK letters, a 34D sits between the sister sizes 32DD (firmer band, same cup volume) and 36C (easier band, same cup volume).

Sister sizes earn their keep when your calculated band feels too snug or too loose, or when your exact size is sold out. They are a useful approximation rather than a perfect swap, since brands cut differently. Find yours in seconds with the sister size calculator, or learn the logic in our sister sizes guide.

Common Measuring Mistakes

  • Measuring over everyday clothes. Even a t-shirt adds bulk under the tape. Measure against bare skin or a thin, unpadded bra for numbers you can trust.
  • Letting the tape ride up at the back. The tape must stay horizontal all the way round. If it angles upward behind you, the reading comes out too small — a mirror is your best friend here.
  • Mixing up standing and leaning bust numbers. Pick one posture for the simple two-measurement method (standing is standard) rather than blending readings taken different ways.
  • Clinging to a long-held size. If you've worn the same size for years without re-measuring, the size may have been wrong all along — or your body may have changed since. Fresh measurements beat old habits.
  • Treating the calculator result as the final answer. It is the best size to try first, not a guarantee. Cup shape, wire style and fabric all influence fit, so try the calculated size alongside its sister sizes.

Frequently Asked Questions

How do UK bra sizes differ from US bra sizes?

Band numbers are identical in both systems — a 34 band is a 34 band. The difference is in the cups: the letters match from AA to DD, then diverge. The UK continues with E, F, FF, G, GG, H, HH and J, while the US uses DDD, G, H, I and J. So a US DDD is roughly a UK E, and a US G is roughly a UK F.

Is a UK F cup the same as a US F cup?

No — and this is one of the most confusing points in bra sizing. In UK sizing, F is the cup after E (the 7th cup step). In US sizing, F is rarely used at all; many US brands jump from DD to DDD and then to G. If a label says F, check which sizing system the brand follows before comparing.

Why does UK sizing use double letters like FF and GG?

It is simply the UK convention for cups above F: after F comes FF, after G comes GG, and after H comes HH. Each step still represents roughly one more inch of difference between bust and band. The US system reaches the same volumes with single letters instead (G, H, I, J), which is why the letters stop matching above DD.

Are UK and US band sizes the same?

Yes. Both systems measure the band in inches and use the same even numbers — 28, 30, 32, 34 and so on — so a 34 band means the same underbust range in the UK and the US. Only the cup letters differ.

What UK size should I buy if I normally wear a US 34DDD?

Start with a UK 34E, which holds roughly the same cup volume as a US 34DDD on the same band. Use the comparison table on this page as a starting point, then check the specific brand's own size chart — UK brands do not all cut identically.

Why does the same UK size fit differently between brands?

There is no single enforced standard for bra sizing, so each brand grades its patterns slightly differently. Fabric, cup shape, wire length and band elasticity all affect fit too. Two bras labelled 34E can genuinely fit differently, which is why trying the size — and its sister sizes — matters more than the label.

How can I tell if my bra band fits properly?

A well-fitting band sits level around your body, feels snug on the loosest hook when new, and stays in place when you lift your arms. You should be able to slide about two fingers under it — more than that usually means the band is too big. Most of a bra's support comes from the band, not the straps.

Can I use the calculator if I measured in centimeters?

Yes. Choose Centimeters in the unit dropdown and enter your measurements as taken — the calculator converts them to inches first, then applies the UK sizing system. UK bands and cups are inch-based, so the conversion step keeps everything consistent.

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