Volts to Joules Calculator

Volts alone do not convert to joules, because voltage is energy per unit charge. You need one more quantity: either current and time, or electric charge. Use E = V x I x t (volts times amps times seconds), or E = V x Q (volts times coulombs). Both give energy in joules.

There are two main formulas. (1) E (joules) = V (volts) x I (amps) x t (seconds) — power multiplied by time. (2) E (joules) = V (volts) x Q (coulombs) — voltage multiplied by electric charge. For a battery, Q in coulombs = capacity in amp-hours x 3600.

No — not without more information. One volt equals one joule per coulomb, so volts only become joules when multiplied by a charge (coulombs). If you only know volts and amps, you also need the time; if you only know volts and milliamp-hours, that is enough (mAh converts to coulombs).

A typical 9V alkaline battery rated at 500 mAh stores 0.5 amp-hours = 1800 coulombs, so 9 V x 1800 C = 16200 J (about 16.2 kJ or 4.5 Wh). Real capacity depends on brand and discharge rate, so treat this as the rated (nominal) energy.

Multiply: E (J) = V x mAh / 1000 x 3600. The mAh/1000 gives amp-hours and x3600 converts amp-hours to coulombs. Example: a 3.7 V, 3000 mAh phone cell holds 3.7 x 3 x 3600 = 39960 J (about 11.1 Wh).

Use E = 1/2 x C x V squared, with capacitance C in farads and voltage V in volts. Example: a 1000 uF capacitor charged to 50 V stores 0.5 x 0.001 x 2500 = 1.25 J. (Note: a 1000 uF 50 V capacitor is physically large — a small electrolytic that size would typically be rated for much lower voltage.)

Watts-to-joules needs power (watts) and time (E = P x t) and never asks for volts. Volts-to-joules needs voltage plus current and time (E = V x I x t), so it also tells you the electrical power involved. Use the voltage mode when you know volts and amps; use our kW to joules calculator when you only know power and time.

A joule is the same unit either way — what differs is how you get there. Mechanical energy comes from force and distance (E = F x d, e.g. newton-meters), while electrical energy comes from voltage and charge (E = V x Q). Use this calculator for electrical energy; for force-times-distance use a newton-to-joules calculator.

One volt equals one joule per coulomb. So 1 volt applied to 1 coulomb of charge gives 1 joule; applied to 2 coulombs it gives 2 joules. Without a charge value there is no single answer.

Divide joules by 1000 to get kilojoules (kJ), and divide by 3600 to get watt-hours (Wh). Example: 16200 J = 16.2 kJ = 4.5 Wh.

A joule per coulomb is a volt. That is the definition: voltage is the energy delivered per unit of electric charge.

For DC the formula E = V x I x t is exact. For AC, use RMS voltage and RMS current and multiply by the power factor (cos phi), so E = V_rms x I_rms x cos(phi) x t. This calculator assumes DC or resistive AC (power factor = 1).

Rated capacity (mAh) is measured under specific lab conditions. High discharge current, cold temperature, aging, and internal resistance all reduce the usable charge, so real delivered energy is typically 5-20% below the nominal rating.

Use seconds to get joules directly. If you have hours, convert first (hours x 3600 = seconds). Alternatively, compute watt-hours (V x I x hours) and multiply by 3.6 to get kJ (1 Wh = 3,600 J = 3.6 kJ; e.g. 4.5 Wh = 16.2 kJ) — this calculator handles the conversion automatically.