Cup sizes guide: what a bra cup letter actually means

A "D cup" is not one size. In our UK/US model, each cup step represents another inch between bust and band, so a D cup on a 30 in band and a D cup on a 40 in band hold very different amounts. The letter only means something once you know the band beside it.

The cup letter progression

**One inch of difference, one letter**Generated by the Bra Atlas engine using UK/US inch-based steps. The other columns are label conversions. AU follows Berlei through H and A Bra That Fits at HH; some brands keep UK letters. Japan is approximate. “n/a” means outside our table, not an unavailable size.
Difference	cm	UK	US	EU / FR	AU / NZ	Japan (approx.)
0 in	0.0	AA	AA	AA	AA	A
1 in	2.5	A	A	A	A	B
2 in	5.1	B	B	B	B	C
3 in	7.6	C	C	C	C	D
4 in	10.2	D	D	D	D	E
5 in	12.7	DD	DD	E	DD	F
6 in	15.2	E	DDD	F	E	G
7 in	17.8	F	G	G	F	H
8 in	20.3	FF	H	H	G	I
9 in	22.9	G	I	I	H	n/a
10 in	25.4	GG	J	J	HH	n/a
11 in	27.9	H	K	K	n/a	n/a

Measure my size Full sister-size chart

By Rai Ansar · Sizes computed by the Bra Atlas engine · Sources and checked dates · How the sizes are calculated

Start with the band as well as the letter. If you already have a size, the sister-size chart shows how its cup-volume category changes labels on another band.

Up to DD, UK and US agree

Both countries use the same letters from AA through DD. One cup past that, the ladders split.

A UK 34DD and a US 34DD are the same size. One inch of difference more, the UK calls it E while the US calls it DDD; the UK then keeps doubling letters (F, FF, G, GG) while the US moves to a new run (G, H, I, J). A handful of US brands print E for DD and F for DDD instead of using the double letters, which is why a US "E" and a UK E are not reliably the same size (see the E cup page for the worked example).

The EU, French, Australian and Japanese numbers here are printed band labels, not your underbust in centimeters: UK 32 converts to EU 70, France 85, AU 10 and Japan 70. Measurement-based charts can use other rules, so follow the brand’s own chart when shopping. The full band tables are on the international size chart.

Why the same letter means a different size

A cup letter fixes the gap between bust and band, not the band itself. Change the band and the letter's actual volume changes with it.

Going down one band (2 in) and up one cup letter keeps the same cup volume: 34D, 32DD and 36C all hold the same amount, on three different bands. That is the whole idea behind sister sizes, and it is why a D cup on a small band and a D cup on a large band are not comparable sizes, even though the letter is identical. Our own size pages show this directly: 30D, 34D and 38D are three different bodies that all carry a D cup.

Explore the published cup guides

What each letter means, its conversions by band, and sister sizes. This list includes only the guides published so far.

Other tools

Sources

Each source was opened and checked on the date shown, or on 25 September 2026. Where sources disagree, the page says so instead of picking one silently.

Wikipedia, "Bra size": UK and US cup ladders, the +4 method, EN 13402 and JIS cup steps
A Bra That Fits calculator (community calculator of r/ABraThatFits): we submitted 18 measurement pairs in 6 systems on 25 September 2026; raw synthetic fixture outputs are linked from the methodology
Berlei Australia, size charts: AU band = underbust row, cups A to H with no FF or GG
OneMall, "Japanese Bra Size Conversion" (11 September 2026): JIS cups in 2.5 cm steps; JP letter about one above the US letter
Wacoal, "International Size Guide": UK AA to GG paired with US AA to J; AUS/NZ keeps FF and GG; band and cup rows are separate, not a stock list (opened 13 October 2026)