Try the smaller sister size if your band rides up or feels loose, and the larger one if the band digs in but the cups fit.
How the bra size calculator works
BraSizeCalc uses the inch-based method most US and UK brands publish. The band is your underbust rounded to the nearest even inch (modern method), or, if you choose the traditional method, rounded to the nearest inch with 4 added for an even number and 5 for an odd one. The cup is the bust measurement minus the band, rounded to the nearest inch, with one letter per inch. Centimetre measurements are divided by 2.54 first. EU bands are 70 for a 32 and go up 5 for each band size; French bands are EU + 15; Australian bands are the inch band minus 22.
Cup letters by bust minus band
| Difference | US | UK | EU |
|---|---|---|---|
| under ½ in | AA | AA | AA |
| 1 in | A | A | A |
| 2 in | B | B | B |
| 3 in | C | C | C |
| 4 in | D | D | D |
| 5 in | DD | DD | E |
| 6 in | DDD | E | F |
| 7 in | G | F | G |
| 8 in | H | FF | H |
| 9 in | I | G | I |
| 10 in | J | GG | J |
| 11 in | K | H | K |
| 12 in | L | HH | L |
| 13 in | M | J | M |
| 14 in | N | JJ | N |
| 15 in | O | K | O |
Band sizes
| Underbust (in) | Band US/UK | EU | FR | AU |
|---|---|---|---|---|
| 27–29 | 28 | 60 | 75 | 6 |
| 29–31 | 30 | 65 | 80 | 8 |
| 31–33 | 32 | 70 | 85 | 10 |
| 33–35 | 34 | 75 | 90 | 12 |
| 35–37 | 36 | 80 | 95 | 14 |
| 37–39 | 38 | 85 | 100 | 16 |
| 39–41 | 40 | 90 | 105 | 18 |
| 41–43 | 42 | 95 | 110 | 20 |
| 43–45 | 44 | 100 | 115 | 22 |
Brands cut differently, so treat the result as a starting size and check the fit: the band should be level and firm, the centre gore should sit flat and the cups should not gap or spill. Sizes past DD vary most between brands.
Frequently asked questions
What is the sister size of 34C?
32D (band down, cup up) and 36B (band up, cup down).
What is the sister size of 36DD?
34E in UK sizing (34DDD in US) and 38D.
Do sister sizes fit the same?
The cup holds the same volume, but the band and wire width change, so the fit is close rather than identical.
Is BraSizeCalc free?
Yes, with no sign-up or ads.
Are my measurements saved or sent anywhere?
They are saved in this browser only and never leave your device.