British bra sizes follow the inch system: the band is your underbust in inches and the cup letter grows with each inch of difference between bust and band, with extra double letters in the series. This calculator turns your tape-measure readings into a UK size and shows the equivalent in the US, Australia and Europe.
How to use the UK bra size calculator
- Measure the underbust: a soft tape around the ribcage directly below the breasts, snug and level.
- Measure the bust: around the fullest part, level and not tight.
- Enter both in inches or centimetres.
- Read your size. If a result feels wrong, try the neighbouring band and the sister size.
UK bra size formula
cup number = bust − band, in inches (rounded to the nearest inch)
UK cup = AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K, KK for 0 to 16
The UK cup scale is taken from the table on Wikipedia’s bra measurement page (retrieved 2026-10-15), where British brands such as Panache, Freya and Fantasie use the sequence AA-A-B-C-D-DD-E-F-FF-G-GG-H-HH-J-JJ-K-KK. The conversions match the Brava and Fantasie size charts used on the Bra Size Converter (US/UK/EU/AU/FR/JP) page.
| Bust − band (in) | UK cup | US cup | EU / FR cup letter |
|---|---|---|---|
| <1 | AA | AA | AA |
| 1 | A | A | A |
| 2 | B | B | B |
| 3 | C | C | C |
| 4 | D | D | D |
| 5 | DD | DD/E | E |
| 6 | E | DDD/F | F |
| 7 | F | G | G |
| 8 | FF | H | H |
| 9 | G | I | I |
| 10 | GG | J | J |
| 11 | H | K | K |
| 12 | HH | L | L |
The Australian band is the UK band minus 22 (Brava, Berlei). Australian cups run AA, A, B, C, D, DD, E, F, G, H without the double letters after DD (Wikipedia and Berlei’s centimetre chart), so a UK FF is an Australian G. The European band in centimetres is 60 + 2.5 × (UK band − 28).
Worked example
Underbust 32 in, bust 38 in.
- Band: 32. Difference: 38 − 32 = 6 inches, which is cup E on the UK scale.
- UK size: 32E. US: 32DDD/F. Australia: 10E. Europe: 70F.
Common reasons a size feels wrong
- Band too loose: a band that rides up at the back means the band is too large; go down one band and up one cup.
- Cup wrinkles or gaps: the cup is too large or the wrong shape.
- Spillage: the cup is too small; go up a cup letter.
- Brand cut: the same size can fit differently between brands, so try the neighbouring sizes.
Use the Cup Size Calculator for the European approach, and the Band Size Calculator if you only need the band. This page is general information, not a professional fitting.
Sources
Every figure above comes from these pages, read directly on the dates shown. Brand names are used only to identify published charts.
- Wikipedia — Brassiere measurement (UK, US and Australian cup letters; underbust method) — checked 2026-10-15
- Brava Lingerie — bra size chart (Australian and UK bands) — checked 2026-10-15
- Fantasie — size guide (UK, European band conversion) — checked 2026-10-15
- Berlei (Rebel) — Australian bra size guide (cm) — checked 2026-10-15
Frequently asked questions
How do I calculate my UK bra size?
Round your snug underbust measurement to the nearest even number of inches for the band, then subtract it from your bust measurement. Each inch is a cup size: 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = E, 7 = F, 8 = FF, 9 = G and so on.
Why are there double letters in UK cups?
British brands insert DD, FF, GG, HH, JJ and KK between the single letters so that the steps stay one inch apart. Wikipedia lists the UK cups as AA-A-B-C-D-DD-E-F-FF-G-GG-H-HH-J-JJ-K-KK-L.
Should I add 4 inches to my band?
That older method, still seen in some shops, adds four inches to the underbust. A 2012 University of Portsmouth study that Wikipedia cites compared it with professional fitting, and modern UK specialists measure the underbust directly, as this calculator does.
How do I convert my UK size to other countries?
The US band is the same and the cup letters match up to DD; the Australian band is the UK band minus 22. The European band is in centimetres. The results show them all, and the Bra Size Converter (US/UK/EU/AU/FR/JP) goes the other way.
What if my measurement is between two sizes?
Try both. If the band measurement sits halfway between two even numbers, try the smaller band with a larger cup (the sister size) as well as the larger band; see the Sister Size Calculator.