Bra Size Calculator — Find Your Correct Bra Size
Calculate your bra size from band and bust measurements in inches. Shows cup size, band size, and sister sizes for alternative fits. See also our Clothing Size Converter and Ring Size Converter.
How to Measure Your Bra Size
- Measure your band size: wrap a tape measure snugly around your ribcage, just under your bust.
- Round to the nearest even number for your band size.
- Measure your bust: wrap the tape around the fullest part of your bust.
- Subtract the band measurement from the bust measurement.
- Each inch of difference equals one cup size (1"=A, 2"=B, 3"=C, etc.).
Formula
Band Size = Round under-bust measurement to nearest even number
Cup Size = Bust Measurement - Band Size
1" = A, 2" = B, 3" = C, 4" = D, 5" = DD
Example
Under bust: 34 inches (band = 34)
Bust: 37 inches
Difference: 37 - 34 = 3 inches = C cup
Result: 34C
Sister sizes: 36B (up) and 32D (down)
Bra Size Chart
| Difference (in) | US Cup Size | UK Cup Size |
|---|---|---|
| 0" | AA | AA |
| 1" | A | A |
| 2" | B | B |
| 3" | C | C |
| 4" | D | D |
| 5" | DD/E | DD |
| 6" | DDD/F | E |
| 7" | G | F |
| 8" | H | FF |
Frequently Asked Questions
What are sister sizes?
Sister sizes have the same cup volume but different band sizes. Going up a band size means going down a cup size, and vice versa. For example, 34C = 36B = 32D in cup volume.
How often should I get measured?
Bra size can change due to weight fluctuations, hormonal changes, pregnancy, and aging. Re-measure every 6-12 months or when your current bras feel uncomfortable.
Why do US and UK sizes differ?
US and UK sizing systems diverge after D cup. The UK uses DD, E, F, FF, G while the US uses DD, DDD, G, H. Always check which system a brand uses.
Should the band be tight?
The band should be snug but comfortable on the loosest hook. You should be able to fit two fingers under it. The band provides 80% of the support.
What if I am between sizes?
Try both sizes and sister sizes. Different brands fit differently. The best fit has a smooth cup with no gapping or spillage, and the band sits level around your body.