Joules to Volts Calculator

Divide the energy by the charge that carried it: V = J / Q, with charge in coulombs. If 24 joules of work moves 2 coulombs through a component, the potential difference across it is 12 V. The formula is the definition of the volt itself: one volt is one joule of energy per coulomb of charge.

No. Joules measure energy and volts measure potential difference, which are different physical quantities, so there is no fixed conversion factor between them. The link is the charge involved: voltage is energy per unit charge. That is why this calculator needs both the energy in joules and the charge in coulombs to produce a voltage.

The coulomb is the SI unit of electric charge, equal to the charge carried by about 6.24 x 10^18 electrons. It is also the charge that flows when a current of one ampere runs for one second, so charge in coulombs equals current in amps multiplied by time in seconds. That relationship is often the route to finding Q for this calculation.

A battery's voltage states how much energy it gives each coulomb of charge it pushes around a circuit. A 9 V PP3 battery does 9 joules of work per coulomb, and a 12 V leisure battery does 12 joules per coulomb. Multiply voltage by the total charge delivered and you get the energy supplied in joules.

Be careful: V = J / Q applies to charge moved at a constant potential difference. A capacitor's voltage falls as it discharges, so its stored energy is E = 0.5 x C x V squared, or equivalently E = 0.5 x Q x V, with the factor of a half reflecting the changing voltage. Using J / Q on a capacitor gives only half the actual peak voltage, because the stored energy reflects the average voltage during discharge, not the starting voltage.