Depends on the engine, transmission gearing, etc... more information would be useful. I'd highly recommend you read the POST in my signature to help you get the most out of your time here. It has tips on searching sailnet, writing a good post, etc.. Welcome to the asylum.
You must state the motor and the gearbox reduction and the direction of rotation of the prop, and the shaft size and the shaft taper.
If you don't know the gearbox reduction, mark the flywheel and the final drive shaft and turn the flywheel until the final drive turns exactly once. Count the rumber of flywheel turns it needs to do it.
The Volvo MD17C turns the final drive shaft once for every 1.92 turns of the flywheel (the crankshaft, effectively).