Here is the size chart for selecting Watery Duncan wetsuits for men. For these wetsuits, your chest, height, and weight are considered when finding your correct size.
If you happen to fall between two sizes, choose the size that aligns with most of the measurements, but generally, the most important measurements are weight and chest size.
Ideally, a wetsuit should not fit too loosely. If there are many air pockets or "bags" around the suit, it is too large for you.