| | Re: measuring the leg length on outboards?
Yes, you measure from the underside on the motor mount to the cavitation plate BUT, understand that in the case of kicker motors especially, the measurement will not come to a nice round number like 15 inches or 20 inches.
In the case of OMC motors I know that a 15" shaft length motor will measure about 17-1/2" and a 20" (long) shaft motor will measure about 22-1/2". This is because historically, the cavitation plate was designed to be UNDER water, below the bottom of the transom.
Interestingly enough, larger Mercury outboards have always measured shorter, even on motors they made decades ago.
Shaft length is a rough figure and every motor has the provision for vertical adjustment for installation variation and fine tuning purposes.