Skip to content
Omnikalc

Bra size calculator: find your band and cup size

Find your bra size from two measurements, your underbust and bust, with US, UK and European equivalents.

Updated on
Your inputs

Value out of range

Value out of range

Results

Band size (US and UK)

32

Bust minus band (each inch is one cup size)

4 in

Cup D
Same band in European sizing (EU)
70

The two measurements

You need a soft tape measure and a bra without padding, or no bra.

  • Underbust (band): measure snugly around your ribcage, directly under your bust, keeping the tape level and exhaling.
  • Bust: measure loosely around the fullest part of your bust, with the tape level across your back.

How the size is calculated

  1. Band size: round the underbust to the nearest even number of inches. A 31.5-inch underbust becomes a 32 band.
  2. Cup size: subtract the band from the bust. Each inch is one cup size: 1 in = A, 2 in = B, 3 in = C, 4 in = D, 5 in = DD.

Worked example

Your underbust is 32 in and your bust is 36 in.

  1. Band: 32.
  2. Difference: 36 − 32 = 4 in: D cup.
  3. Your starting size is 32D.
  4. In European sizing the same label is a 70D.

Cup letters in the US and UK

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

Sister sizes

Cup letters are relative to the band. Going down one band and up one cup keeps a similar cup volume: 34C, 32D and 36B are sister sizes. If a band rides up but the cups fit, try one band smaller and one cup larger.

Why sizes vary

There is no single standard. Some US brands still use the old "+4" method, which adds 4 or 5 inches to the underbust for the band. It gives a larger band and smaller cup letter: the same person might be a 32D by the modern method and a 36A by the old one. That is why fit matters more than the label.

Checking the fit

  • The band should be level and snug on the loosest hook, so you can tighten it as it stretches.
  • The center panel should lie flat against your breastbone.
  • The cups should contain the breast without gaps or spilling.
  • The straps should carry only a small part of the support; most comes from the band.

Frequently asked questions

How do I measure my bra size?

Measure snugly around your ribcage, just under your bust, for the band. Then measure loosely around the fullest part of your bust, keeping the tape level. Round the underbust to the nearest even number; each inch of difference between the bust and that band is one cup size.

What cup size is a 4-inch difference?

A 4-inch difference between your bust and band is a D cup: 1 inch is A, 2 inches B, 3 inches C, 4 inches D and 5 inches DD.

What is a sister size?

A sister size has the same cup volume on a different band. Going down a band size means going up a cup, and the reverse: 34C, 32D and 36B have similar cup volumes.

Why do different brands give me different sizes?

There is no single standard. Some US brands still add 4 or 5 inches to the underbust, UK and US cups differ above D, and European sizes use centimeters. Use the calculator as a starting point and check fit: the band should sit level and snug on the loosest hook.

Was this calculator helpful?

Thanks for your feedback!

Results are estimates provided for information purposes. They do not replace professional advice.

Related calculators