The equation for voltage can be written as the current multiplied by the resistance. Voltage is defined as the electric potential energy at a given point in an electric field or circuit, according to About.com.
The SI unit for voltage is the volt or one joule per coulomb. Voltage is considered a scalar quantity, which means the measurement has no directional components, only magnitude. An alternate formula that can be used to calculate voltage is power divided by current. Voltage can also be defined as the electric potential energy per unit charge. The volt was named after the Italian physicist Alessandro Volta.