Table to estimate the approximate propeller diameter
Find the HP of the engine in the X-axis, then report up this power data line until it matches with the RPM on the propeller, (that means the rpm of the engine divided into the gearbox ratio). At the crossing point, go to the left axis and there you will have the corresponding propeller diameter in mm or inches.
This table is aproximated for 3 BLADED propellers with a Radio Area = 0.5.
For 4 BLADED propellers with a Ratio Area = 0.65, take the result and decrease it in a 6%.