Cup Size Calculator — Find Your Bra Cup Letter

Q: How is cup size calculated?

Subtract your under-bust measurement from your bust. The difference equals the cup letter: 1 inch = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = DDD (or E in UK), and so on.

Q: Is cup size the same across brands?

No. Brand fit differs. Use a brand size chart and read fit reviews.

Q: Why does cup volume change with band?

Cup volume increases with band size. A 34D cup holds more than a 32D cup, even though both are labelled D.

Q: What is the largest cup size?

Cups go all the way to N or O in some brands. Most major brands stop at G or H, but full-bust specialty brands like Panache go to K or KK.

Q: What is the difference between AA and A cup?

AA cup is one cup smaller than A. The difference between under-bust and bust is less than 1 inch for AA.

mybrafit. Find your perfect fit

🇺🇸 English

English Español Português Français Deutsch Italiano Nederlands Polski Русский 中文日本語 한국어 Indonesia Tiếng Việt ไทย العربية हिन्दी Türkçe

Find my size

Cup Size Calculator

Find your cup letter in seconds. Enter your under-bust and bust, and we calculate the cup difference for US, UK, EU, and India.

Bra-Size Calculator

Find your perfect fit in seconds

Under bust (in)

Snug under your breasts, parallel to floor.

Bust (in)

Around fullest part, loose, no compression.

Sizing system

Your size in US

30D

Band 30" · Cup D

Sister size ↑

32C

If band feels tight

Sister size ↓

28DD

If band feels loose

💡

For most accurate results, measure in the morning wearing a non-padded bra. Sister sizes are alternates with the same cup volume — try both if the calculator size feels off.

How Cup Size is Calculated

Cup size is the difference between your bust measurement and your under-bust measurement. Each inch of difference equals one cup letter:

Difference	US Cup	UK Cup	EU Cup
< 1 inch	AA	AA	AA
1 inch	A	A	A
2 inches	B	B	B
3 inches	C	C	C
4 inches	D	D	D
5 inches	DD	DD	E
6 inches	DDD	E	F
7 inches	G	F	G
8 inches	H	FF	H

Why Cup Volume Changes With Band

A common myth: "a D is a D." In reality, a 34D holds significantly more than a 32D. Each band size adds about half an inch to the cup width, so cup volume increases as the band increases. This is why sister sizes work the way they do.

Cup Size FAQs

How is cup size calculated?

Subtract your under-bust measurement from your bust. The difference equals the cup letter: 1 inch = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = DDD (or E in UK), and so on.

Is cup size the same across brands?

No. Brand fit differs. Use a brand size chart and read fit reviews.

Why does cup volume change with band?

Cup volume increases with band size. A 34D cup holds more than a 32D cup, even though both are labelled D.

What is the largest cup size?

Cups go all the way to N or O in some brands. Most major brands stop at G or H, but full-bust specialty brands like Panache go to K or KK.

What is the difference between AA and A cup?

AA cup is one cup smaller than A. The difference between under-bust and bust is less than 1 inch for AA.