There are three primary dimensions used to describe inboard boat propellers, which can be used to derive the performance of the prop for a specific application.
Those measurements are diameter, pitch and cup. These are typically listed in the following format:
XX" x YY" .ZZZ
XX is the total overall diameter of the prop measured in inches. This is the size of the complete circle the prop makes when rotating.
YY is the pitch of the prop measured in inches. Pitch is the total theoretical distance in inches the prop would travel through the water when completing one full revolution if no slippage occurred.
ZZZ is the cup of the propeller blades, measured in thousands of an inch.
These three measurements do not tell everything there is to know about a propeller and how it will perform, but they do provide a baseline for comparing two or more different propellers to one another.