A bra size chart gives your size as band + cup: the band is your underbust rounded to an even number, and the cup is bust minus underbust (1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD). Example: a 31″ underbust and 35″ bust gives band 32, 4″ difference = 32D.
A bra size chart pairs your band size with your cup size, using your underbust and bust measurements. Measure both, subtract, and read your size straight off the chart.
This guide gives you the bra size chart, the bra cup size chart, a bra size calculator method, sister sizes, US vs UK vs EU conversions, and fixes for common bra fit problems.
Your cup size is the gap between your bust and underbust. Each inch adds one cup letter, as JCPenney also explains.
Difference (inches)
Cup Size
0
AA
1
A
2
B
3
C
4
D
5
DD / E
6
DDD / F
7
G
8
H
Bra Size Calculator
Use this simple formula: Bust − Underbust = Cup Size. Then add your band size.
Bust
Underbust
Difference
Bra Size
35″
31″ → band 32
4″
32D
37″
33″ → band 34
4″
34D
36″
33″ → band 34
3″
34C
41″
37″ → band 38
4″
38D
Bra Sister Size Chart
Sister sizes keep the same cup volume but change the band. Go down one band and up one cup for a tighter fit. Go up one band and down one cup for a looser fit.
Your size
Tighter band
Looser band
32D
30DD
34C
34C
32D
36B
36C
34D
38B
38B
36C
40A
When to use a sister size:
Band rides up: go down a band, up a cup.
Band digs in: go up a band, down a cup.
Only fits on the tightest hook: try a smaller band and larger cup.
I am the admin and author of SizesForm, researching, verifying, and explaining measurements, dimensions, weights, and sizes in simple terms to help readers understand everyday comparisons accurately and confidently.
