Bra size calculator
Enter your measurements to find your cup size in French, American and British systems.
Bra size combines two measurements: underbust (in cm, giving the FR size: 80, 85, 90…) and cup (letter A, B, C… corresponding to the difference between bust and underbust). A 90B = 90 cm underbust, B cup.
Proper fit depends on both band and cup. A band too loose rides up the back (loses support). A cup too small spills. Studies show 80% of women wear the wrong size. Measuring correctly transforms comfort.
- Underbust: measure horizontally just under the bust (no bra or unpadded), exhale normally.
- Bust: measure at the fullest point, unpadded bra, without compressing.
- Calculate the difference: that gives the cup.
- The underbust rounded to nearest 5 is your FR size.
Cups by bust difference
| Bust − under-bust difference (cm) | FR / EU | US | UK |
|---|---|---|---|
| ≤ 10 | AA | AA | AA |
| 11-12 | A | A | A |
| 13-14 | B | B | B |
| 15-16 | C | C | C |
| 17-18 | D | D | D |
| 19-20 | E | DD | E |
| 21-22 | F | DDD | F |
| 23-24 | G | DDDD | G |
| ≥ 25 | H | F | H |
Frequently asked questions
How is the cup calculated?
Cup = bust - underbust. Difference of 10 cm = AA, 12 = A, 14 = B, 16 = C, 18 = D, 20 = E, 22 = F, 24 = G.
Difference between FR, US, UK sizes?
Underbust: FR uses cm (80, 85, 90…), US/UK use inches (32, 34, 36…). US cups use a different system above D (D, DD, DDD instead of D, E, F in France).
Signs my bra does not fit?
Band riding up back = band too loose. Straps digging shoulders = band too loose. Bust spilling (sides, top, bottom) = cup too small. Cup wrinkling = cup too big.
Do I need to resize during pregnancy?
Yes, breast volume changes. Generally +1 to +2 band sizes and +1 to +2 cups during pregnancy. Prefer wireless bras and elastic bands late pregnancy.