It depends on the radius of any given edge of the conductor, and how much voltage is on it. That's why conductors on electrostatic equipment are usually very smooth and round. You don't see wiring on them because wire is generally too small of diameter to hold a great deal of voltage. The less leakage there is, the more voltage can build up. In any case, there is more to read on the Internet and in books about this, so if you need to, go for it.
Voltage is like pressure.
You would measure water or air pressure in pounds per square inch. What you are dealing with doesn't change, its behavior does. Voltage is only one facet of electricity. It's because of the pressure you can create with your finger. The volume of water you shoot is very small, but the pressure is high.