Here's the size chart for choosing the Watery Calder Rapid wetsuit for men. The measurements are taken with the suit lying flat and unstretched. The wetsuit will adjust both during use and in the water, adapting to your body while swimming. Therefore, select the size that closely matches your measurements.
If you find yourself between two sizes, choose the one that meets most of the measurements. Generally, the most important measurements are chest and height (ankle to shoulder).
A wetsuit shouldn't fit too loosely, so if you notice a lot of air pockets or "bunching" around the suit, it's too large for you.