• If your over-arm measurement is more than 7" larger than your chest measurement, choose a suit one size larger than your chest.
• Suits have what is called a "drop," which is the difference between the size of the jacket and the size of the pants. Classic-fit suits typically have a 6" drop, meaning that a size 38R jacket is paired with size 32 pants. Trim-fit and extra-trim-fit suits typically have a 6" to 7" drop.
• Suit makers usually leave enough extra fabric at the seams to allow pants to be let out by 1" to 2". Pants can always be taken in.