Instrumentation

If the rotating shaft is part of a motor, read the nameplate.

Otherwise count the revolutions made by the shaft in one minute. This will give you the speed of the shaft in revolutions per minute. (RPM)

Please provide some meaningful information if you'd like an better answer.

Thanks but is not part of a motor. The shaft is part of an old and small water turbine that I cleaned and I want to test it in a small river and test the output in RPM and TORQUE or HP.

RPM, HP and torque will be totally dependent on flow into the turbine wheel.

RPM will be easy to do visually. For starters I'd look for a roughly equivalent commercially available water wheel and see what the manufacturer says about power generation of the wheel. (mechanical, not electrical)

Calculating the output of an uninstrumented wheel will be VERY difficult and is far beyond my meager capabilities. _{(ten fingers/10 toes)}

Good luck with the project! Sounds like fun.

1. Calculation of Hydro Power - Hydro

1. Introduction to Water Wheels - Hydro
   
2. Building a Waterwheel - Hydro
   
3. Design calculations for no-head, low-head waterwheels by Rudy ...
   
4. Water Wheel Engineering

lyn's comment is valid. I hope you can see the differences between the most we can provide you and the least.