Bra Size Calculator: Find Your Real Size in 60 Seconds (US, UK, EU)

Here's a secret most of us learn the hard way: the size printed on your bra might not be your size at all. Professional fitters see the same mistake every day, a band that's too loose and a cup that's too small. The good news? You only need a soft tape measure and one minute to fix it.

Use the free bra size calculator below. Enter two quick measurements and get your size in US, UK, EU, French, Australian and Japanese/Korean sizing, plus your sister sizes.

How to measure your bra size at home

Wear a thin, unpadded bra or nothing at all. Stand tall in front of a mirror so you can see the tape stays level all the way around.

1. Underbust (band): wrap the tape around your ribcage right under your breasts. Breathe out and pull it snug, not painful. This number decides your band.
2. Bust (cup): measure around the fullest part of your chest, usually across the nipples. Keep the tape loose enough that it doesn't squash anything.
3. Enter both numbers in the calculator above and pick inches or centimeters.

Measure twice and use the average. If you are close to your period, your bust can be fuller than usual, so measure again a week later to compare.

How this bra size calculator works

There is no magic, just simple math that fitters use every day:

• Band: your underbust in inches, rounded to the nearest even number (28, 30, 32, 34...). The old "add 4 inches" trick came from a time when bras were made of stiff, non-stretch fabric. Modern bras stretch, so most fitters skip it.
• Cup: each inch of difference between your bust and band is one cup size. One inch is an A, two is a B, three is a C, and so on.
• EU, French, Australian and Asian sizes are converted from your US/UK size with the standard brand charts. A US 32 band is an EU 70, a French 85 and an Australian 10, and every step up adds 5 (EU and France) or 2 (Australia). Cups match the US up to D, then Europe continues with E, F and G.

Bust minus band	US cup	UK cup
1 in	A	A
2 in	B	B
3 in	C	C
4 in	D	D
5 in	DD	DD
6 in	DDD/F	E
7 in	G	F
8 in	H	FF

US vs UK vs EU bra sizes: why your size changes when you shop abroad

US and UK bands use the same numbers, but the cups split after DD. The US goes DDD, G, H. The UK goes E, F, FF, G. So a US 34DDD is a UK 34E. In Europe your band is in centimeters, so a 34C is roughly a 75C. In Japan and Korea, you'll often see the cup first, like C75, and cups grow in slightly bigger steps. That's why a size that fits perfectly in New York can feel off in Seoul or Paris, and why the calculator gives you every version at once.

What are sister sizes?

A cup letter doesn't mean the same volume on every band. A 32D and a 36D hold very different amounts. Sister sizes keep the same cup volume while changing the band: go down one band, go up one cup. So 34C, 32D and 36B all share roughly the same cup volume.

This trick is gold when your size is sold out, or when the band feels a little too tight or too loose but the cups are perfect.

Signs your new size really fits

• The band sits level all the way around and feels snug on the loosest hook.
• The center piece (the gore) lies flat against your chest.
• No gaps at the top of the cup and no spilling over the edge.
• The underwire sits behind your breast tissue, not on top of it.
• The straps stay put without doing all the work. About 80% of the support should come from the band.

Want the full mirror test? Our bra fitting guide walks you through every fit problem and how to fix it.

Why your bra size changes

Your body isn't a fixed number. Weight changes, your monthly cycle, pregnancy, breastfeeding, new workout routines and simply getting older can all shift your size. Re-measure every 6 to 12 months, or any time your favorite bra suddenly feels wrong.

Your size, your style

Once you know your real size, the fun part starts. Lingerie that fits doesn't just feel better, it looks expensive and makes you stand a little taller. Explore the 6 lingerie styles every woman should know, find the cuts that flatter you most in lingerie for every body type, and keep your new favorites beautiful with our lingerie care guide.

Bra size calculator FAQ

Is an online bra size calculator accurate?

It's a reliable starting point because it uses the same measurements a fitter takes. Brands cut differently, though, so always confirm with the fit checks above.

What if I'm between two sizes?

Try both. If you're between bands, the tighter band with a bigger cup often gives better support. If you're between cups, stretch lace and molded cups are more forgiving.

Should I add 4 inches to my band measurement?

Usually not. That rule was made for old, rigid bras. Most modern fitters use your actual underbust, rounded to an even number.

Can I measure myself while wearing a bra?

Yes, as long as it's unpadded and not a push-up. Padding adds inches to your bust and pushes your cup size up.