Bra Size Calculator
Calculate your bra size from band and bust measurements in inches or cm.
Returns US, UK, EU, French, and Australian sizes with sister size suggestions.
Bra sizing uses two measurements — band size and cup size — to find a correctly fitting bra. Poor fit is extremely common; studies suggest 70–80% of women wear the wrong bra size.
The Measurement Formula:
Step 1: Band Size Measure ribcage directly under the bust (in inches), round to nearest even number.
If measurement is odd, add 1 inch. If even, add 0 inches (some brands add 2 — check brand guidelines).
Band size = ribcage measurement (rounded to nearest even number)
Step 2: Cup Size Bust measurement (fullest point) minus Band size = Cup difference
| Difference (inches) | Cup Size |
|---|---|
| 0–0.5" | AA |
| 1" | A |
| 2" | B |
| 3" | C |
| 4" | D |
| 5" | DD / E |
| 6" | DDD / F |
| 7" | G |
Worked Example:
- Under-bust measurement: 34 inches → Band size = 34
- Bust measurement: 38 inches
- Difference: 38 − 34 = 4 inches → Cup size = D
- Result: 34D
Sister Sizing: Going up one band size and down one cup volume gives the same cup volume:
- 34D = 36C = 32DD (all hold the same volume of breast tissue)
Use sister sizing when your exact size is unavailable.
Practical Tips:
- Measure without a bra, or with a non-padded bra
- The band should be snug on the loosest hook when new — as the bra stretches, move to tighter hooks
- Underwire should lie flat against the ribcage, not sit on breast tissue
- Cup spillage = go up a cup size. Empty cup = go down a cup size