What is my bra size?
Measure snugly under the bust and loosely around the fullest part, in inches or centimetres. See a starting US and UK size to try on.
- US size
- 32D
With a 32 in underbust and a 36 in bust, your starting US size is 32D.
- UK size
- 32D
- Band (in)
- 32
- Cup difference (in)
- 4
US size: 32D. With a 32 in underbust and a 36 in bust, your starting US size is 32D.
How to calculate
Computes a starting bra size in US and UK sizes from underbust and bust measurements, with one cup letter for each inch the bust is larger than the band.
Example with the default inputs (Underbust 32 in, Bust 36 in, Band method Underbust): With a 32 in underbust and a 36 in bust, your starting US size is 32D.
Method: band = underbust in whole inches, up to the next even number (or + 4 if even, + 5 if odd, by the older method); cup = bust in whole inches − band, one letter per inch.
- Measurements round to the nearest whole inch, halves up. Centimetres convert at 2.54 cm to the inch first.
- US cups: 1 in A, 2 B, 3 C, 4 D, 5 DD, 6 DDD, 7 G, 8 H, 9 I, 10 J, 11 K. UK cups: 5 DD, 6 E, 7 F, 8 FF, 9 G, 10 GG, 11 H. A difference of 0 is AA.
- Sizes differ between brands. The result is a starting size to try on, not a fit.
Worked examples
Each example is checked against the calculator on every build.
- Underbust 32 in, Bust 36 in, Band method Underbust gives US size 32D, UK size 32D, Band (in) 32, Cup difference (in) 4.Source: hand calculation in content.mdx: band 32 (even); 36 − 32 = 4 in = D
- Underbust 33.4 in, Bust 40 in, Band method Underbust gives US size 34DDD, UK size 34E, Band (in) 34, Cup difference (in) 6.Source: hand calculation in content.mdx: 33.4 rounds to 33, odd, so band 34; 40 − 34 = 6 in = US DDD, UK E
- Underbust 31 in, Bust 38 in, Band method Add 4 or 5 in gives US size 36B, Band (in) 36, Cup difference (in) 2.Source: hand calculation in content.mdx: 31 is odd, so 31 + 5 = 36; 38 − 36 = 2 in = B
- Underbust 29.53 in, Bust 35.43 in, Band method Underbust gives US size 30DD, UK size 30DD, Band (in) 30, Cup difference (in) 5.Source: hand calculation in content.mdx: 75 cm = 29.53 in → 30; 90 cm = 35.43 in → 35; 35 − 30 = 5 in = DD
How it works
- Convert each measurement to inches (1 in = 2.54 cm) and round to the nearest whole inch. A value exactly halfway rounds up; to absorb float noise, a value within 0.000000001 of a half counts as the half.
- Band:
- Underbust method (the default): the rounded underbust, raised to the next even number if it is odd.
- Plus-four method: the rounded underbust + 4 if it is even, or + 5 if it is odd.
- Cup difference = rounded bust − band.
- Cup letter from the difference:
| Difference (in) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| US | AA | A | B | C | D | DD | DDD | G | H | I | J | K |
| UK | AA | A | B | C | D | DD | E | F | FF | G | GG | H |
A difference below 0 (the bust smaller than the band) or above 11 has no size here.
The result is a starting size. Brands differ, and fit depends on shape as well as size.
Worked examples by hand
Underbust 32 in, bust 36 in. The band is 32 (already even). 36 − 32 = 4 in, so 32D in both the US and the UK.
Underbust 33.4 in, bust 40 in. 33.4 rounds to 33, which is odd, so the band is 34. 40 − 34 = 6 in: 34DDD in the US, 34E in the UK.
Underbust 31 in, bust 38 in, plus-four method. 31 is odd, so the band is 31 + 5 = 36. 38 − 36 = 2 in, so 36B.
Underbust 75 cm, bust 90 cm. 75 ÷ 2.54 = 29.53 in, which rounds to 30 (even), so the band is 30. 90 ÷ 2.54 = 35.43, which rounds to 35. 35 − 30 = 5 in, so 30DD.
Other questions people ask
How do I measure for a bra?
Stand straight with a soft tape and no padded bra. For the underbust, wrap the tape snugly around your rib cage just under the bust, level all the way round. For the bust, wrap it loosely around the fullest part, also level.
How is the cup size worked out?
Round both measurements to whole inches. The cup is the bust minus the band: 1 in is A, 2 in B, 3 in C, 4 in D, 5 in DD, and so on, one letter per inch. A 32 in band with a 36 in bust is 4 in, so 32D.
What is the plus-four method?
An older US method adds 4 in to an even underbust, or 5 in to an odd one, to get the band. The same measurements then give a band 4 or 5 sizes larger and a smaller cup letter. Many fitters now use the underbust itself; try both if one does not fit.
Why do US and UK cup letters differ?
They agree up to DD. After that, the US goes DDD, G, H, and the UK goes E, F, FF, G, GG, H. A 6 in difference is a US DDD and a UK E.
Why does my size differ between brands?
There is no single binding standard for US and UK bra sizes, and brands cut their bands and cups differently. Treat the result as a size to start trying on. A band that rides up or a cup that gaps or spills means trying a size either side.
What about EU and French sizes?
EU sizes measure in centimetres and step 2 cm per cup under the European standard EN 13402-3, so the letters do not line up with US and UK letters. Use the brand’s own size chart to convert.