>>337450979
Almost, the number is the band size and cup size is determined by the difference (subtracted) between overbust and underbust 
So if the overbust is 40 inches and the underbust is 36 inches then the band size is 36 inches and the difference is 4 inches, and D is 4 inches, C is 3 inches, etc
[spoiler]I'm 36D[/spoiler]