Voltage multiplier calculations
Higher the capacitance, more energy is stored, so be carefoul. As the roule of The rule of thumb is to take a range from 10nF to 100nF. And don't forget to add the load of at least 40MOhm.

Output voltage (once when it is settled) is 2*Vmax*N where N is the number of diode-capacitor sections.

You can find more explanation on:

http://www.cirvirlab.com/index.php/tutorials/90-diode-voltage-multiplier-circuit.html

and insted of calculating, you can simulate voltage multiplier on

http://www.cirvirlab.com/simulation/diode_voltage_multiplier_circuit_online.php