How to calculate power of a generator
Power is calculated in Watts. Usually generators are sold on KVA. So you need to calculate your building load or your device wattage; then you can simply convert the KVA to KW by dividing KVA by 0.8 and you will get the KW. As the unit of electricity is in KWH so simply 1 KW is equal to 1 KWH. Here 0.8 is power factor.

Now moving towards your question: It looks like that you are trying to make a generator. We have made a motor in university. That was totally a trail and error method.

Else, you can visit this link for further help regarding load calculation, HP of motor, 3 phase generator. http://www.dieselserviceandsupply.com/Power_Calculator.aspx