Cup sizes guide: what a bra cup letter actually means

A "D cup" is not one size. Every cup letter is the gap between your bust and your band, in one-inch steps, 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. Rows past DD are where UK and US labels split.
Difference	cm	UK	US	EU / FR	AU / NZ	Japan
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

Measure my size Full sister-size chart

By Rai Ansar · Sizes computed by the Bra Atlas engine, sources checked 26 September 2026 · How this page was made

"cup sizes guide" gets about 110,000 Google searches a month in the US and "cup sizes" 33,100 more (Google Ads and DataForSEO Labs data, 26 September 2026). No page we found in the top results explains that the letter is relative to the 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).

Every other country relabels the same two numbers, band and cup, rather than measuring anything differently: EU and Japan use the underbust in centimetres, France adds 15 to the EU band, and Australia subtracts 22 from the UK band. 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.

Every cup letter, on its own page

What the letter means, how it reads in every system by band, sister sizes, and the misconceptions we found in other sizing guides.

C cup size gets 27,100 US searches a month but its results are dominated by shopping pages, and A cup has no measurable search volume of its own; we did not build pages for either.

Other tools

Sources

Each source was opened and checked 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 output is in our repository
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