Bra Size Calculator

Bra size calculator at a glance#

A bra size calculator turns two tape measurements into a band number and a cup letter. The band size is your underbust measurement, taken around the ribcage just below the breasts and rounded to a whole number. The cup size is the difference between your bust measurement and that band number.

To work it out by hand, measure your underbust for the band, then measure your bust and subtract the band from the bust. Each inch of difference is roughly one cup: a 1 inch difference is an A cup, 2 inches a B, 3 inches a C, 4 inches a D, and 5 inches a DD. In US sizing a DD is the same as an E, and a DDD is the same as an F.

Worked example: if your underbust is 32 inches, your band size is 32. If your bust is 35 inches, the difference is 3 inches, which is a C cup, so your size is 32C. A 34 inch underbust with a 38 inch bust gives a 4 inch difference, a D cup, for a 34D.

Enter your bust and underbust measurements in the calculator above for your exact band and cup. Round your underbust to the nearest whole number, and treat the result as a starting point: bodies and brands vary, so sister sizes such as 34C, 32D and 36B can fit similarly, and trying the bra on is the real test of fit.

Two ways brands set the band#

The answer block above sets your band equal to your underbust measurement rounded to a whole number. Some brands and fitters use the older +4 method instead: round your underbust to the nearest even number and add 4 inches. A 31 inch underbust becomes a 30 in the even-rounding step, then a 34 band. The +0 method gives you a 31, rounded up to an even 32 band.

Both methods are in use, which is one reason the same person can be a 32 in one brand and a 34 in another. If a band feels too tight, size up the band and down a cup letter to keep the same volume. If it rides up at the back, the band is too loose.

How to measure your band#

Wrap a soft tape around your ribcage directly under your bust, where the band of a bra sits. Keep the tape level and snug but not tight, and breathe out. Read the number in inches and round to the nearest whole number. That figure is your band in the +0 method used by the calculator above.

How to measure your bust#

Wrap the tape around the fullest part of your bust, usually across the nipples, with the tape level front and back. Stand upright and do not pull the tape tight. Subtract your band number from this bust number: each inch of difference is one cup. A 3 inch difference is a C, a 4 inch difference is a D. In US sizing a DD equals an E and a DDD equals an F.

Sister sizes#

Sister sizes share the same cup volume across neighbouring bands. Going up one band size and down one cup letter keeps the volume the same: a 34C, a 32D and a 36B all hold a similar cup. If your calculated size is sold out or fits oddly, a sister size is the first thing to try.

US, UK and EU differences#

US and UK band numbers match in inches, but the cup letters diverge above a D because the UK adds DD, E, F, FF and so on rather than the US DD, DDD, G run. EU bands use centimeters: a US 32 band is roughly an EU 70, a 34 is an EU 75, a 36 is an EU 80, each step being 5 cm. Australian band sizes are the US band minus 22, so a US 34 band is an Australian 12. Letters never convert perfectly between systems, so check a brand size chart when buying abroad.

Frequently asked questions#

How do I find my bra size at home?#

Measure your underbust for the band and your bust for the cup, then subtract the band from the bust. Each inch of difference is one cup size: 1 inch is an A, 3 inches a C, 4 inches a D. Enter both numbers in the calculator above for the exact band and cup.

What does a well-fitting band feel like?#

The band should sit level around your body and stay put when you raise your arms. You should be able to slide two fingers under it at the back, no more. Fasten a new bra on the loosest hook so you can tighten it as the elastic stretches.

How do I measure the correct cup size?#

Measure around the fullest part of your bust with the tape level, then subtract your band number. The inch difference is your cup: 2 inches is a B, 4 inches a D, 5 inches a DD (E). Use that with your band to read the size, for example a 34 band with a 4 inch difference is a 34D.

What is sister sizing?#

Sister sizes hold the same cup volume in a different band. Move up one band and down one cup, or down one band and up one cup: 34C, 32D and 36B are sister sizes. Try one when your usual size is unavailable or the band feels off.

How often should I remeasure?#

Remeasure whenever the fit changes or after weight change, pregnancy or a few months of regular wear, since band elasticity loosens over time. Bras generally hold their support for 6 to 12 months of frequent wear.

What is the difference between a plunge and a push-up bra?#

A plunge bra has a low centre cut for deep necklines and adds little volume. A push-up bra has padding at the bottom of the cup to lift and centre the bust. Both come in the same band and cup sizing, so your measured size applies to either.