Bra Size Calculator
Find your bra size from two measurements: underbust and bust. Get your US, UK and EU size, the matching sister sizes and tips for checking the fit. Example: 32 inch underbust and 36 inch bust is a 32D.
Show steps
How to use the Bra Size Calculator
- Measure around your ribcage directly under the bust with a soft tape, snug but level.
- Measure around the fullest part of your bust while standing, with the tape level and not tight.
- Enter both numbers and choose inches or centimeters.
- Press Calculate and try the size plus the sister sizes.
Formula and method
Band = underbust rounded to the nearest even number. Cup = bust minus band: 1 inch is A, 2 is B, 3 is C, 4 is D, 5 is DD (E), 6 is DDD (F in US sizing), and so on. Sister sizes keep the same cup volume: go up a band size and down a cup, or down a band and up a cup.
Worked example: 32 inch underbust, 36 inch bust
| Step | Value |
|---|---|
| Underbust | 32 in, so band 32 |
| Bust minus band | 36 – 32 = 4 in |
| Cup | D |
| Size | 32D |
| Sister sizes | 34C and 30DD |
Bust minus band to cup size
| Difference | US cup | UK cup |
|---|---|---|
| 1 in | A | A |
| 2 in | B | B |
| 3 in | C | C |
| 4 in | D | D |
| 5 in | DD or E | DD |
| 6 in | DDD or F | E |
| 7 in | G | F |
| 8 in | H | FF |
How to check the fit
The band should sit level and snug, with room for two fingers. The center gore should lie flat against your breastbone. Breast tissue should fill the cups without spilling over or gaping, and the straps should carry only a small part of the support. If the band rides up, try a smaller band and a bigger cup.
Frequently asked questions
How do I measure my bra size?
Measure your underbust for the band and your fullest bust for the cup, then subtract the band from the bust. Each inch of difference is one cup size.
What is a sister size?
A size with the same cup volume but a different band, such as 34C and 32D. Use it when the band feels too tight or loose.
Why does my size differ between brands?
Brands cut bands, cups and wires differently, and sizing standards differ between countries.
Should I measure with or without a bra?
Without a bra or in a thin unlined one, standing upright, for the most accurate result.
How often should I re-measure?
Every six months to a year, and after weight changes, pregnancy or nursing.
What is the UK to US difference?
Bands match. US cups run A, B, C, D, DD, DDD or F, G, while UK cups go DD, E, F, FF, G.
Sources
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