Joules to Volts Calculator
Convert joules to volts using charge, or capacitance — with the reverse calculation too.
Charge needed to carry 60 J
| At voltage | Charge | Equivalent |
|---|---|---|
| 1 V | 60 C | 16.6667 mAh |
| 5 V | 12 C | 3.3333 mAh |
| 12 V | 5 C | 1.3889 mAh |
| 24 V | 2.5 C | 0.6944 mAh |
| 48 V | 1.25 C | 0.3472 mAh |
| 120 V | 0.5 C | 0.1389 mAh |
| 240 V | 0.25 C | 0.0694 mAh |
Volts are joules per coulomb
Voltage is not a quantity of energy — it is energy per unit charge. So joules on their own cannot become volts; you need the charge that carried them:
V = E ÷ Q
60 J carried by 5 coulombs is 12 V. The same 60 J carried by 10 coulombs is only 6 V.
Capacitors are the other common case
A charged capacitor stores energy that depends on the square of the voltage:
E = ½ C V², so V = √(2E ÷ C)
Note the square: doubling the voltage on a capacitor stores four times the energy. That is why capacitor banks are charged as high as their rating allows, and why a failure at high voltage releases so much energy at once.
Charge units in practice
Batteries are rated in mAh rather than coulombs. The
conversion is 1 mAh = 3.6 C, since one amp for one hour is 3,600
coulombs. A 3,000 mAh cell holds 10,800 C, so at a nominal 3.7 V it stores about
40,000 J — roughly 11 Wh.
Battery energy is usually quoted in watt-hours, which already accounts for voltage. Comparing mAh across cells of different voltage is meaningless; compare Wh instead.