Calculate properties of electric generator?
There are two popular types of generators, wound-rotor synchronous generators and permanent-magnet synchronous generators. Permanent-magnet commutator machines may have some popularity with hobbyists, but they are not commercially popular.

To calculate the voltage of a synchronous generator, you need to determine the armature form factor, winding distribution factor, flux distribution factor and pitch factor. You also need the total flux provided by the field magnets or wound field. You also need the rotor speed and the number of armature conductors through which the field passes during each rotation. An appropriate factor for units of measurement is also required. The voltage is the product of all of the factors mentioned.

A description of the essentials of designing a wound-field synchronous generator and determining all of the design factors requires about 90 pages in a text book. Some additional background material may be required for full understanding.

Commutator Machines

Commutator machines are a bit more complicated, but the essentials are similar.