Watts to Joules Calculator - Power over Time

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard electrical engineering formulas

Watts are joules per second. Multiply watts by seconds and you get joules. The formula is clean, but only if the power is steady or you are using average power.

Formula at a glance

  • J = W x seconds
  • W = J / seconds
  • Wh = W x hours

Field note: The number gets huge fast because joules are small. That is normal, not a calculator bug.

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Watts to Joules Calculator

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Formula

J = W × s

How to use the Watts to Joules Calculator

Use this as a unit check for energy, power and time. Keep the time period honest, because a one-hour run and a one-month run can make the same load look completely different.

Worked example

Example: 60 W for 10 seconds uses 600 J. The same 60 W for one hour is 216,000 J, or 60 Wh.

Practical checks before you trust the number

  • Use seconds for joules, hours for watt-hours.
  • Pulsed loads need average power over the chosen time window.
  • For battery and bill work, Wh or kWh is usually easier than joules.

Common mistake

The number gets huge fast because joules are small. That is normal, not a calculator bug.

Sources and references

Related calculators

Frequently Asked Questions

Joules = watts × seconds. Energy equals power times time. Example: 100 W for 60 seconds → 6000 J. This is the inverse of joules-to-watts, useful for calculating energy delivered or stored over a known duration.

E (joules) = P (watts) × t (seconds). Same as the inverse: power times time gives energy. Example: 200 W for 10 seconds → 2000 J. For longer durations in hours, multiply by 3600 to convert to seconds first.

J = W × s = 100 × 60 = 6000 J. So 100 watts running for 60 seconds delivers 6000 joules of energy. That's about 1.67 watt-hours, or 0.00167 kWh. Same formula scales to any wattage and runtime.

Because energy is power integrated over time. Joules alone are an absolute amount of energy; watts alone are a rate. To get joules from watts, you must specify how long the rate was sustained. Without time, the conversion is undefined.

Power (W) is the rate of doing work; energy (J or kWh) is the total work done. Power tells you how fast energy is delivered or used; energy tells you the cumulative amount. A 1000 W heater running 1 hour delivers 1 kWh, or 3.6 million joules. Both numbers describe the same energy, just in different units.

Yes, the conversion works for any electrical device with a known wattage and runtime. A 60 W light running 10 minutes uses 60 × 600 = 36,000 J = 36 kJ. This is useful for energy auditing and for engineering pulsed-load calculations on capacitors or batteries.

Yes. The watts × seconds product gives joules of energy transferred. For longer durations, convert hours to seconds (×3600) first, or use kWh directly for residential loads. This is the standard way to quantify energy in physics and electronics, even when bills are in kWh.