Bra size calculator with UK, US, EU, French and Australian sizes
Enter your underbust and bust measurements in inches or centimetres and this bra size calculator returns your band and cup in UK, US, EU, French and Australian labels, plus the neighbouring sister sizes. UK sizing is also what most Indian brands use, so the UK result doubles as the India size.
Treat the answer as a starting point. Brands cut bands and cups differently, so the best size is the one that fits on the loosest hook, with the centre panel flat against your breastbone. The calculation runs in your browser and nothing is stored or sent anywhere.
How to use the Bra Size Calculator
- Choose Inches or Centimetres.
- Measure the underbust snugly around the ribcage directly under your bust, with the tape level at the back.
- Measure the bust around the fullest part, keeping the tape level and not squashing the tissue.
- Read your size in the big result, and the other countries’ labels underneath.
- Try the sister sizes if the band feels too tight or loose, then copy your sizes to use when shopping.
Bra Size Calculator features
Five sizing systems
UK, US, EU, French and Australian band and cup labels from one pair of measurements.
UK and US letters kept apart
The UK uses double letters (DD, FF, GG) where the US uses other letters from a 5 inch difference upwards, so the calculator shows both.
Sister sizes
Two steps up and down the band with the cup volume held steady.
Inches or centimetres
Switching the unit converts what you have already typed.
How the calculation works
The cup letters follow the table on Omni Calculator’s bra size page (read 19 October 2026). The letters match through D; at a 5 inch difference the US says DD/E, Australia DD and the UK DD; at 8 inches the US says H, Australia G and the UK FF. The page you are reading is an estimate built from those published charts, not a brand fitting.
- Band: the underbust is rounded to the nearest even number of inches (an odd value such as 33 in rounds up to 34). Charts such as Debra’s list the same UK and US band numbers for both countries.
- Cup: the band is subtracted from the bust. Each inch of difference is one cup size: 1 in is A, 2 in is B, 3 in is C, 4 in is D, and so on.
- Other countries: a UK band of 34 is EU 75, French 90 and Australian 12 (EU = (band − 4) × 2.5, French = EU + 15, Australia = UK − 22). EU and French cup letters run through the alphabet, one per inch, so UK DD is EU E.
| Bust minus band | UK | US | AU | EU / FR |
|---|---|---|---|---|
| 3 in | C | C | C | C |
| 4 in | D | D | D | D |
| 5 in | DD | DD/E | DD | E |
| 6 in | E | DDD/F | E | F |
| 7 in | F | DDDD/G | F | G |
| 8 in | FF | H | G | H |
| 9 in | G | I | H | I |
Sister sizes explained
Sister sizes hold the cup volume steady while the band changes. Going up one band size (2 in) means going down one cup letter, and the reverse. So 34D has the same cup volume as 32DD and 36C. If your band feels too tight but the cups fit, try the sister size with the larger band; if the band rides up, try the smaller band with the larger cup.
European brands size the band directly from the underbust in centimetres, so a European size recommended by a European brand’s own chart can differ from the converted label here. Where they disagree, trust the brand’s chart and a trial fitting.
Limits and fit tips
The charts stop at a 17 in difference and a 58 in band. Measurements change with weight, pregnancy, breastfeeding and the time of the month, so re-measure when your body changes. If you are in doubt, a specialist fitter is more accurate than any calculator. For other garments see the clothing size converter and the blouse measurement chart.
Bra Size Calculator FAQ
How do I calculate my bra size in inches?
Round your underbust to the nearest even number for the band, then subtract it from your bust measurement. One inch of difference is an A cup, two is B, three is C and four is D.
What is the difference between UK and US cup sizes?
They match up to D. From a 5 inch difference the UK uses DD, E, F, FF, G while the US uses DD/E, DDD/F, DDDD/G, H, I, so the same cup can carry different letters.
What are sister sizes?
They are sizes with the same cup volume on a different band, such as 34D, 32DD and 36C. Go up a band and down a cup, or the reverse.
Is the India bra size the same as the UK size?
Most Indian brands label bands in inches in the same way as UK and US sizes, but cup letters and fit vary, so check each brand’s chart.
Why does my size differ between brands?
Brands cut bands, cups and fabrics differently, and stretch varies. A calculator gives a starting point; the right size is the one that fits on the loosest hook.
Should I measure with or without a bra?
Measure over a thin, unpadded bra or without one, so padding does not add to the bust measurement.