Bra Size Guide — Calculating Band and Cup, and How Countries Differ
How to calculate the underbust band and cup that make up a bra size, the difference in cup steps between Korea/Japan (2.5 cm) and Europe (2 cm), UK and US DD/E/F labels, and sister sizes.
A bra size such as ‘75B’ contains two pieces of information. 75 is the underbust circumference (band), and B is the difference between bust and underbust (cup). If you measure both accurately, you can convert to most systems. For how to measure, see How to measure your body.
Band: underbust circumference
Korea, Japan and Europe state the underbust circumference in 5 cm steps. An underbust of 73–77 cm is 75. Other countries label the same band like this.
| Korea, Japan, Europe | France, Spain | Italy | UK, US |
|---|---|---|---|
| 65 | 80 | 1 | 30 |
| 70 | 85 | 2 | 32 |
| 75 | 90 | 3 | 34 |
| 80 | 95 | 4 | 36 |
| 85 | 100 | 5 | 38 |
France adds 15 to the European value, and Italy uses the European value divided by 5, minus 12.
Cup: how many cm per step
This is where countries differ the most.
- Korea and Japan: a 10 cm difference is A, and each cup adds 2.5 cm (7.5 = AA, 12.5 = B, 15 = C …).
- Europe (EN 13402): a 10–12 cm difference is AA, 12–14 cm is A, and each cup adds 2 cm.
So a person with a 12.5 cm difference is a B by the Korean standard and an A by the European standard. Even if the two labels differ by a letter, both can be right. The SIZE ATLAS converter calculates according to each system's definition, so this difference shows up as it is.
UK and US cup letters
| Europe | UK | US |
|---|---|---|
| D | D | D |
| E | DD | DD |
| F | E | DDD |
| G | F | G |
| H | FF | H |
After D, the UK mixes in double letters such as DD, E, F, FF, while the US uses DD, DDD. Some US brands use F instead of DDD, so the larger the cup, the more important it is to check the brand's chart.
Sister sizes
Going down one band size and up one cup gives a similar cup volume. 75B, 70C and 80A are ‘sister sizes’ of each other. If the band is loose but the cup fits, try the sister size with a smaller band and a larger cup.
How to check the fit
- The band should be level with the floor, and on the loosest hook it should allow about one finger underneath.
- The top of the cup should not gap, and the breast should not spill over.
- If the straps carry most of the weight, the band is too loose.
The same size can feel different depending on brand and design (full cup, 3/4 cup, bralette). This article is a general explanation of size systems; if you have pain or any concerns, consult a professional.
Size systems are approximate correspondences based on national standards and industry practice, and can differ by half to one size depending on brand, product and fabric. Always check the brand's own size chart before buying.