Volts to Joules Conversion Calculator

What this calculates

Voltage is energy per unit of charge — that’s its definition. Turn that around and the energy delivered is the charge multiplied by the voltage it moved through. This calculator does that product, giving you the electrical energy in joules for a given amount of charge crossing a fixed potential difference.

It’s the relationship behind a few practical estimates: how much energy a battery delivers as it pushes a known charge at its terminal voltage, roughly how much energy a capacitor dumps during a discharge, and the energy side of physics problems that hand you volts and coulombs.

The volts to joules formula

is energy in joules, is the potential difference in volts, and is charge in coulombs. If you don’t have charge directly, build it from current and time:

with current in amps and time in seconds. A battery supplying 3 A for 20 seconds has moved 60 coulombs.

Worked example

The calculator’s defaults are 12 V and 10 C of charge.

So moving 10 coulombs across a 12-volt difference transfers 120 joules. Put in everyday terms, if that 10 C moved in 5 seconds, the current was 2 A and the power was 24 W — and 24 W for 5 seconds is 120 J, which matches. The two ways of getting to energy agree, as they must.

Volts to Joules Conversion Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

Charge and voltage to energy

Charge	5 V	12 V	48 V	120 V
1 C	5 J	12 J	48 J	120 J
10 C	50 J	120 J	480 J	1,200 J
100 C	500 J	1,200 J	4,800 J	12,000 J
3,600 C (1 Ah)	18,000 J	43,200 J	172,800 J	432,000 J

The bottom row is a battery-sized amount of charge: one amp-hour is 3,600 coulombs, so a 1 Ah cell at 12 V holds about 43,200 J, which is the same as 12 watt-hours.

What the result assumes

The formula treats the voltage as constant while the charge moves. That’s a fair approximation for a battery under a light, steady load, but not for a capacitor charging from empty — a capacitor’s voltage rises as charge piles onto its plates, so its stored energy is ½ × C × V², exactly half of what a constant-voltage product would suggest for the same endpoint. Use this calculator for fixed-voltage transfers, and the capacitor energy formula for anything with a rising or falling voltage.

Common mistakes

Using amp-hours directly as coulombs. Multiply amp-hours by 3,600 first.
Applying V × Q to a charging capacitor. That overstates the stored energy by a factor of two; use ½ C V².
Forgetting the load determines where the energy goes. The joules are delivered regardless; whether they become heat, motion, or chemical change is up to what’s connected.

For the reverse, use the joules to volts calculator. To work from power and time instead of charge, see watts to joules.

About the formula: Use the stated electrical relationship and enter values in the displayed units.

Frequently Asked Questions

How does this volts to joules conversion calculation work?+

It multiplies voltage by charge. The energy transferred when a given amount of charge moves across a fixed potential difference is that charge in coulombs times the voltage, and the product comes out in joules.

Where do I get a charge value in coulombs?+

Charge rarely appears on a label. If you know current and how long it flowed, multiply them: Q = I × t, with current in amps and time in seconds. A device drawing 2 A for 5 seconds has moved 10 coulombs.

How do I convert a battery's amp-hours to coulombs?+

Multiply amp-hours by 3,600. A 10 Ah battery holds 36,000 coulombs of charge. At a nominal 12 V, that's about 12 × 36,000 = 432,000 J, or roughly 120 watt-hours — which matches the usual Wh = Ah × V shortcut.

Does this formula apply to a charging capacitor?+

No. This assumes charge crosses a constant voltage. A capacitor's voltage climbs as it fills, so its stored energy is ½ × C × V², which works out to half of what this simple product would give for the same final charge and voltage.

Is the result electrical energy or heat?+

It's the electrical energy delivered. Where that energy ends up — heat in a resistor, mechanical work in a motor, chemical energy in electrolysis — depends on the load. For a purely resistive load, all of it becomes heat.

What's the difference between this and watts to joules?+

This uses voltage and charge (E = V × Q). Watts to joules uses power and time (E = P × t). Both give energy in joules; pick the one that matches the quantities you actually know.