These calculators will assit you in determining what size generator you may require or how to convert one unit of electricity to another.

Sizing Data - Power Consumption

Generator Size to Start Motors

Instructions: You only need to fill in the columns coloured in blue.
Fill in the HP of the motor(s) in their starting squence, select the start method (Direct On Line or Star Delta) and press Evaluate. The required generator size will then be displayed at the bottom.

3 Phase (415 volt @ 50Hz)
1 Phase (240 volt @ 50Hz)

Source: http://www.macgen.com/calcul.html