In Electrostatics solver, capacitance is calculated between two conductors by simlating the electric field that arises when a voltage differential is applied.
If you want to use field calculator, you can calculate the total electric charge on an object and divid the voltage value.
- Qty -> D (load D vector into the calculator);
- Geom -> Surface… (select the surface of interest) -> OK
- number...->scalar->value: (voltage value)->OK