Your bodysuit size is your bra size if you have a "balanced" figure.
You have a "balanced" figure if:

YOUR BRA SIZE IS AND YOUR BASIC, LOWER-BODY SHAPER SIZE IS
32B, C, D, DD, DDD, G Small
34B, C, D, DD, DDD, G Medium
36B, C, D, DD, DDD, G Large
38B, C, D, DD, DDD, G X-Large
40B, C, D, DD, DDD, G XX-Large
42B, C, D, DD, DDD, G 3X-Large

What To Do If You Don’t Have A “Balanced” Figure:

     • Try a crossover, bodysuit size.

If Your Basic, Lower-Body Shaper Size Is One Size Too Large,

     • Add 2 to your bra band size and move down one letter in your cup size.

     • Using a size 36C as an example, its crossover size would be a 38B.

If Your Basic, Lower-Body Shaper Size Is One Size Too Small,

     • Subtract 2 from your bra band size and move up one letter in your cup size.

     • Using a size 38C as an example, its crossover size would be a 36D.