Both sizing methods
Switch between the modern measure and round method and the older plus four inches method, so you can compare what different brands still use.
Free tool, no sign up
Bra Size Calculator
Enter your underbust and bust measurements to get your true band and cup size in seconds, plus sister sizes and instant US, UK, EU, French, Australian and Japanese conversions.
Bra size calculator tool
Your measurements
Measure over a thin, non-padded bra. Results update as you type.
Measurement unit
in
in
Your estimated size
32CUS sizing
- Band
- 32
- Cup
- C
- Difference
- 3.0 in
International conversions
- US32C
- UK32C
- EU / DE70C
- FR / ES85C
- AU / NZ10C
- JP70C
Sister sizes to try
- 30D
- 34B
Fit tip: the band should sit level and firm on the loosest hook, with two fingers slipping under it.
Why this bra size calculator is different
Most size checkers give you one number and stop. This one shows the full picture, including the sizes that will actually fit you on a bad day.
Sister sizes included
Every result comes with the size up and the size down in band, so you always have two backup options when a style runs small or large.
Six size systems
US, UK, EU, French, Australian and Japanese sizes are calculated at the same time, which makes online shopping from any store far easier.
Inches and centimetres
Switch units at any point and your numbers convert with you. Nothing is lost and nothing has to be re-entered.
Live fit guidance
The result panel explains what your band to bust difference means and flags measurements that look like a tape problem rather than a size.
Private and instant
Everything is worked out in your browser. No account, no email, no measurements sent anywhere, and no waiting for a page to reload.
How to measure your bra size
Two measurements are all you need. Use a soft tape, stand upright, and breathe normally while you measure.
Measure your underbust
Wrap the tape directly under your bust, level all the way round and snug enough that it stays put when you drop your arms. Note the number.
Measure your bust
Run the tape across the fullest part of your bust without compressing the tissue. Keep it parallel to the floor and let it rest lightly.
Enter both numbers
Type or slide the two values into the calculator and pick inches or centimetres. Your band, cup and international sizes appear instantly.
Try your sister sizes
Take your main size and the two sister sizes into the fitting room or the basket. Cut and brand vary, so the closest fit wins.
What a correct bra size actually changes
Less shoulder and back strainA firm band carries most of the weight, so the straps stop digging in and the load comes off your shoulders.
Clothes sit properlyThe right cup volume removes gaping, spillage and the wrinkling that shows through fitted tops and dresses.
Fewer returns onlineKnowing your UK and EU equivalents means you order the right label size first time from international stores.
Bras last longerA band that fits on the loosest hook has room to tighten as the elastic relaxes over months of washing and wear.
| Difference | US cup | UK cup | EU cup |
|---|---|---|---|
| Under 1 in (2.5 cm) | AA | AA | AA |
| 1 in (2.5 cm) | A | A | A |
| 2 in (5 cm) | B | B | B |
| 3 in (7.5 cm) | C | C | C |
| 4 in (10 cm) | D | D | D |
| 5 in (12.5 cm) | DD | DD | E |
| 6 in (15 cm) | DDD | E | F |
| 7 in (18 cm) | G | F | G |
| 8 in (20 cm) | H | FF | H |
| 9 in (23 cm) | I | G | I |
| 10 in (25 cm) | J | GG | J |
Bra size calculator questions
How do I know what bra size I am?
Measure snugly under your bust for the band and loosely across the fullest part for the bust, then enter both numbers above. The band comes from your underbust measurement rounded to an even number, and each full inch of difference between bust and band moves the cup up one letter.
Should I add 4 inches to my underbust measurement?
Not usually. The plus four inches rule dates from an era of far less stretchy fabrics and tends to produce a band that is too loose and a cup that is too small. Modern fitters measure and round, which is the default here, but the traditional method is included because a few older brands and charts still follow it.
What are sister sizes and when should I use them?
Sister sizes hold the same cup volume while changing the band. Going down a band size moves the cup up a letter, and going up a band size moves it down a letter, so 34C, 32D and 36B all hold a similar volume. Use them when the cup fits but the band feels tight or loose, or when your exact size is out of stock.
Why does my bra size change between brands?
Cup depth, wire width, strap placement and fabric stretch are not standardised, so a size in one brand can fit like a sister size in another. Treat the calculator result as your starting size, then adjust up or down a band or cup depending on how a specific style is cut.
How do US, UK and EU bra sizes compare?
UK and US bands use the same numbers, but the cup letters split after D. A US DD is a UK DD, while a US DDD is a UK E. EU bands are in centimetres, so a US 34 band becomes an EU 75 and a French 90, and EU cups run straight through the alphabet with E where the US uses DD.
How often should I measure again?
Check every six to twelve months, and sooner after weight changes, pregnancy, breastfeeding, hormonal changes or a new exercise routine. Also remeasure when a bra you like starts fitting only on the tightest hook, because that is the band elastic wearing out rather than your size changing.
How do I tell if my current bra is the wrong size?
The clearest signs are a band that rides up your back, straps that dig in or slip constantly, wires sitting on breast tissue rather than on the ribcage, cups that gape at the top or spill over the edge, and marks that stay on your skin long after you undress.
Get your size, then try your sister sizes
Take one minute with a tape measure and you will stop guessing at labels for good. Scroll back up, enter your two measurements, and note down all three sizes before your next order or fitting.
This calculator gives a general sizing estimate based on standard fitting charts. Brand cut and personal comfort always come first, and it is not medical advice.