Subtract your band measurement (step 1) from your cup measurement (step 2). Generally, for each inch in difference, the cup goes up by one size.
See the cup size conversion chart here.
Example:
Step 1: 34" under measurement = 38" band
Step 2: 40" over measurement
Step 3: 40" - 38" = 2" or Cup "B"
Your size would be 38B
The cup size calculation starts falling apart at 4 inches larger than your band size, and if you have droopy or pendulous breasts, your measurement will not be accurate.
If The Differtence Is: |
Your Standard Cup Size Is: |
0" to 1/2" (1.3cm) |
AA |
1/2"- 1" (2.6 cm) |
A |
2" (5.1 cm) |
B |
3" (7.6 cm) |
C |
3" (7.6 cm) |
C |
4" (10.2 cm) |
D |
5" (12.7 cm) |
DD * or E * |
5" (12.7 cm) |
DD * or E * |
5" (12.7 cm) |
DD * or E * |
6" (15.2 cm) |
DDD * or F * |
7" (17.8 cm) |
G * |
8" (20.3 cm) |
H * |
9" (22.9 cm) |
I * |
10" (25.4 cm) |
J * |
*Please Note: This bra measuring method becomes very unreliable at bra sizes 38D and larger.