Free tool 06
Bra Size Converter
Convert a bra size between systems or calculate a starting size from your underbust and bust measurements. We also show your sister sizes.
Your result will appear here.
How to measure
- Underbust: measure snugly around your ribcage, directly under the bust, with the tape level.
- Bust: measure loosely around the fullest part of your bust while wearing a non-padded bra.
- Each inch of difference between bust and band is roughly one cup size.
Example: a 31.5 inch underbust and 36 inch bust gives a starting size of 32D (UK).
Good to know
Measuring gives a starting point, not a guaranteed fit. Breast shape, band firmness and brand all change the best size; a professional fitting is the most reliable method.
Reference chart
| UK / US | EU | FR | AU | Underbust in (approx.) | Underbust cm (approx.) |
|---|---|---|---|---|---|
| 28 | 60 | 75 | 6 | 27–28 | 67–72 |
| 30 | 65 | 80 | 8 | 29–30 | 72–77 |
| 32 | 70 | 85 | 10 | 31–32 | 77–83 |
| 34 | 75 | 90 | 12 | 33–34 | 83–88 |
| 36 | 80 | 95 | 14 | 35–36 | 88–93 |
| 38 | 85 | 100 | 16 | 37–38 | 93–98 |
| 40 | 90 | 105 | 18 | 39–40 | 98–103 |
| 42 | 95 | 110 | 20 | 41–42 | 103–108 |
| 44 | 100 | 115 | 22 | 43–44 | 108–113 |
| 46 | 105 | 120 | 24 | 45–46 | 113–118 |
| Bust − band (in) | UK / AU | US | EU / FR |
|---|---|---|---|
| 0 | AA | AA | AA |
| 1 | A | A | A |
| 2 | B | B | B |
| 3 | C | C | C |
| 4 | D | D | D |
| 5 | DD | DD/E | E |
| 6 | E | DDD/F | F |
| 7 | F | G | G |
| 8 | FF | H | H |
| 9 | G | I | J |
| 10 | GG | J | K |
| 11 | H | K | L |
| 12 | HH | L | M |
| 13 | J | M | N |
| 14 | JJ | N | O |
| 15 | K | O | P |
FAQs
What is a sister size?
Sister sizes have the same cup volume on a different band: go down a band and up a cup (32D → 30DD) or up a band and down a cup (32D → 34C).
Why do UK and US cups differ after D?
UK sizing uses double letters (DD, E, F, FF…) while many US brands use DD/E, DDD/F, G, H. So a UK F is usually a US G.
How do EU band sizes work?
EU bands are in centimetres, in 5 cm steps: UK 32 is EU 70 and UK 34 is EU 75. French bands are 15 higher than EU.