# What is my bra size?

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.

- Page: https://www.acalculator.org/everyday-life/bra-size-calculator
- JSON spec: https://www.acalculator.org/everyday-life/bra-size-calculator.json
- Version: 7da2b6d48ed5

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| under | Underbust | Snug around the rib cage, just under the bust. |
| bust | Bust | Loosely around the fullest part of the bust. |
| method | Band method | Use the underbust as the band, or the older method that adds 4 or 5 inches. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| us | US size | The US band and cup. |
| uk | UK size | The UK band and cup (the band is the same as the US band). |
| band | Band (in) | The US and UK band size in inches. |
| difference | Cup difference (in) | The bust, rounded to a whole inch, minus the band. |

## 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.

## Assumptions

- 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

1. under = 0.8128, bust = 0.9144, method = underbust gives us = 32D, uk = 32D, band = 32, difference = 4. Source: hand calculation in content.mdx: band 32 (even); 36 − 32 = 4 in = D.
2. under = 0.84836, bust = 1.016, method = underbust gives us = 34DDD, uk = 34E, band = 34, difference = 6. Source: hand calculation in content.mdx: 33.4 rounds to 33, odd, so band 34; 40 − 34 = 6 in = US DDD, UK E.
3. under = 0.7874, bust = 0.9652, method = plus-four gives us = 36B, band = 36, difference = 2. Source: hand calculation in content.mdx: 31 is odd, so 31 + 5 = 36; 38 − 36 = 2 in = B.
4. under = 0.75, bust = 0.9, method = underbust gives us = 30DD, uk = 30DD, band = 30, difference = 5. Source: hand calculation in content.mdx: 75 cm = 29.53 in → 30; 90 cm = 35.43 in → 35; 35 − 30 = 5 in = DD.

## FAQ

### 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.

## Sources

- Wikipedia, Bra size: US and UK band and cup conventions (one cup per inch of difference; US DD, DDD, G…; UK DD, E, F, FF, G, GG, H…) and the plus-four band method. https://en.wikipedia.org/wiki/Bra_size
- NIST SP 811 (2008), Appendix B: 1 in = 2.54 cm exactly.