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Use this calculator to

  • Calculate the energy transferred when a known charge moves through a potential difference
  • Solve W = QV problems for physics coursework and electrical training
  • Work out the energy a battery delivers per coulomb at its rated voltage
  • Convert between volts, coulombs and joules when checking textbook answers

Volts to Joules Calculator

Convert voltage (V) and charge (C) to energy (J).

V
C
Result
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Formulas

  • J = V × Q (charge in coulombs)

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Joules to Watts

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Stored energy in capacitor banks and surge protection devices is measured in joules, and the figure matters every time an industrial site adds new process equipment. Power factor correction (PFC) capacitor banks rated at 400V and 100 microfarads store enough energy to damage downstream electronics if a discharge path is mis-specified. Engineers signing off a new line need a clean joule figure to compare against the withstand rating of the protective devices already on the supply.

On sensitive process kit (food production, pharmaceutical manufacturing, data centres co-located with offices) the energy in a transient voltage surge determines whether the surge protection device clamps cleanly or fails open. UK installations under BS EN 62305 and BS 7671 specify SPDs by their joule rating and let-through voltage. An accurate volts to joules calculation lets the design engineer match the SPD class to the transient risk on the supply, which in turn determines the warranty position on the protected equipment.

Purely Energy supports manufacturers and commercial property groups whose downtime costs make protection sizing a financial question, not just an electrical one. Our Purely Insights platform monitors voltage events at the meter, giving the asset owner a record of transients that can feed back into capacitor and SPD design. Combined with our MOP and DA/DC services across 2,000+ sites, we provide the operational data engineers need to specify protection that holds up under real UK grid conditions.

Common questions

How do I convert volts to joules?

You cannot convert voltage to energy on its own; you also need the charge that moves. The relationship is W = Q x V: energy in joules equals charge in coulombs multiplied by potential difference in volts. Moving 2 coulombs through 12 V transfers 2 x 12 = 24 joules.

Is a volt the same as a joule per coulomb?

Yes, by definition. One volt is one joule of energy per coulomb of charge, which is exactly why W = Q x V works. A 230 V supply gives every coulomb that flows through a load 230 joules of energy to dissipate as heat, light or motion.

Does W = QV give the energy stored in a capacitor?

Not directly. A capacitor's voltage rises as it charges, so the stored energy is the average over the charging process: W = QV / 2, half of what the simple formula suggests. Use W = QV only where the charge moves through a fixed potential difference, such as a battery or a steady supply.

How do joules relate to kilowatt-hours?

One kilowatt-hour, the unit on an electricity meter, is 3.6 million joules (3.6 MJ): 1,000 watts sustained for 3,600 seconds. Joules suit single events and physics problems, while kWh suits metering, where the quantities are vastly larger. Divide a joule figure by 3,600,000 to express it in kWh.

What is one coulomb of charge?

One coulomb is the charge moved by a current of one amp flowing for one second, equal to about 6.24 x 10^18 elementary charges. A 10 A element passes 10 coulombs every second, so at 230 V it transfers 2,300 joules per second, which is exactly its 2.3 kW power rating.

Related calculators

The conversions that procurement and engineering use alongside this one.

Volts to Joules Calculator | Purely Energy