Bra Size Calculator — measure, convert, find your sister size
Measure your band and bust to get your bra size, then convert it between US, UK, EU, French, Australian and Japanese sizing — sister sizes included.
How to measure: wear an unpadded bra or none, stand relaxed and breathe out. Take the underbust snugly around the ribcage just below the bust, and the bust loosely around its fullest point, keeping the tape level. Cup shape and grading differ between brands — check the brand's own chart before ordering.
Bra band size conversion chart
US and UK label the band in inches, Europe and Japan in centimetres. The cup letter is unaffected by the band system.
| US / UK | EU / JP | FR / ES / BE | AU / NZ | IT | Underbust |
|---|---|---|---|---|---|
| 28 | 60 | 75 | 6 | 0 | 27–29 in · 69–74 cm |
| 30 | 65 | 80 | 8 | 1 | 29–31 in · 74–79 cm |
| 32 | 70 | 85 | 10 | 2 | 31–33 in · 79–84 cm |
| 34 | 75 | 90 | 12 | 3 | 33–35 in · 84–89 cm |
| 36 | 80 | 95 | 14 | 4 | 35–37 in · 89–94 cm |
| 38 | 85 | 100 | 16 | 5 | 37–39 in · 94–99 cm |
| 40 | 90 | 105 | 18 | 6 | 39–41 in · 99–104 cm |
| 42 | 95 | 110 | 20 | 7 | 41–43 in · 104–109 cm |
| 44 | 100 | 115 | 22 | 8 | 43–45 in · 109–114 cm |
| 46 | 105 | 120 | 24 | 9 | 45–47 in · 114–119 cm |
| 48 | 110 | 125 | 26 | 10 | 47–49 in · 119–124 cm |
Bra cup size conversion chart
The cup letter comes from bust minus band. US and UK match up to DD, then diverge; EU, FR and JP run straight through the alphabet.
| Bust − band | US / CA | UK | EU / FR / JP | AU / NZ |
|---|
About the Bra Size Calculator
A bra size is two measurements wearing one label: the band number comes from your underbust, and the cup letter comes from how much bigger your bust is than that band. In US and UK sizing the band is measured in inches and each full inch of difference is one cup letter — a 1 in difference is an A cup, 2 in is B, 3 in is C, 4 in is D, 5 in is DD. That is why the cup letter on its own means nothing: a 30D and a 38D hold completely different volumes, because the band they sit on is four sizes apart.
The systems diverge above D. US sizing continues DD, DDD (sometimes written F), then G, H. UK sizing goes DD, E, F, FF, G, GG — so a US DDD is a UK F, and a UK E has no US equivalent letter at all. European sizing sidesteps the problem by running straight through the alphabet (D, E, F, G) and by labelling the band in centimetres instead of inches: a US 34 band is EU 75, French 90, Australian 12, Italian 3 and Japanese 75. This calculator prints every one of those from a single pair of measurements.
It also lists your sister sizes — the sizes that hold the same cup volume on a different band. Go down one band and up one cup (34C → 32D) or up one band and down one cup (34C → 36B) and the cup itself stays the same size. Sister sizes are what you reach for when the cup fits but the band digs in, or when your size is sold out and you need the closest real alternative. Everything is calculated in your browser; no measurements are sent anywhere.
How to use it
- Measure your underbust: run a tape snugly around your ribcage directly under the bust, keeping it level and parallel to the floor.
- Measure your bust: run the tape around the fullest part of the bust, this time loosely, without compressing.
- Pick inches or centimetres, type both numbers in, and read your US size plus the UK, EU, French, Australian, Italian and Japanese equivalents.
- Already know your size? Switch to "Convert a known size", pick the system and size you own, and see what it is called everywhere else.
- Check the sister sizes before you buy — if the cup fits but the band feels tight, the next band up with one cup letter down is the size to try.
Frequently asked questions
How do I measure my bra size at home?
You need two numbers. Wearing an unpadded bra or none at all, measure snugly around your ribcage just under the bust — that is your underbust or band measurement. Then measure loosely around the fullest part of the bust. Round the underbust to the nearest even number in inches for your band size, and subtract the band from the bust: 1 in difference is an A cup, 2 in a B, 3 in a C, 4 in a D, 5 in a DD, 6 in a DDD.
What is 34B in EU size?
A US or UK 34B is a EU 75B, a French 90B, an Australian 12B, an Italian 3B and a Japanese 75B. The band number changes because Europe labels the band in centimetres (75 cm) while the US and UK label it in inches (34 in); the B cup is the same in all of them.
What is the difference between US and UK cup sizes?
They are identical up to and including D and DD, then they split. US sizing goes DD, DDD (or F), G, H; UK sizing goes DD, E, F, FF, G, GG. So a US DDD is a UK F, a US G is a UK FF, and the UK E sits between the US DD and DDD. Band numbers are the same in both systems, so only the letter needs converting.
What are sister sizes?
Sister sizes are different labels for the same cup volume. Moving down one band size means moving up one cup letter to keep the cup the same: 34C, 32D and 36B all hold a similar volume. Use them when the cup fits but the band is too tight or too loose, or when your exact size is out of stock.
Is 32C bigger than 34B?
They are sister sizes, so the cups hold roughly the same volume — the 32C simply sits on a band that is two inches smaller. Neither is "bigger" overall: the 34B has the looser band, the 32C the tighter one.
Should I add 4 or 5 inches to my underbust measurement?
Not any more. The "add 4 inches" rule dates from an era of much less elastic fabric and now produces bands that are several sizes too loose. Modern fitting uses the underbust measurement itself, rounded to the nearest even number. If your ribcage measures 31 in, start at a 32 band rather than a 36.
Why does the same size fit differently between brands?
Cup shape, wire width, strap placement and fabric stretch all vary between makers, and many brands grade their own way above a D cup. The conversions here follow the standard international charts, so treat the result as the size to try first and check the brand's own size chart before ordering.
Is my data stored?
No. Everything is calculated in your browser. The measurements you type are never uploaded or saved.