The bust measurement is taken at the highest point of the bust, and the underbust measurement is taken directly below the bust.
The difference between the bust and underbust measurements gives the cup size:
Cup size = bust measurement - underbust measurement

As an example calculation:
Size 75 D is calculated as follows:
Chest circumference: 94 cm and underbust circumference: 75 cm
→ therefore, the cup size = 94 cm - 75 cm = 19 cm (this corresponds to cup size D)

 

Size chart for MammaBra®️ - large sizes
Underbust circumference (cm) Bra size (band size)
73-77 75
78-82 80
83-87 85
88-92 90

 

CUP size (Bust measurement - Underbust measurement)
C 16 - 17
D 18 - 19
E 20 - 21