Joules to Watts Calculator

Summary

Convert energy in joules to average power in watts by dividing by time (W = J / s); supports J, kJ, and MJ input units with a reverse check.

How it works

1. Select your input energy unit: joules (J), kilojoules (kJ), or megajoules (MJ).
2. Enter the energy value in the chosen unit.
3. Enter the time duration in seconds over which the energy is delivered.
4. Click Calculate — the tool converts energy to joules, then divides by time.
5. The result is displayed in watts (W), kilowatts (kW), and milliwatts (mW).
6. The reverse section confirms: Power (W) × Time (s) = Energy (J).

Use cases

• Calculate average power output of a battery given its energy capacity and discharge time.
• Size heating elements by converting thermal energy specifications to power ratings.
• Determine average motor power from energy consumed over a known run time.
• Convert solar panel energy yield (kJ) to average power output across a day.
• Verify appliance power ratings from energy audit measurements.
• Engineering homework involving power, energy, and time relationships.
• Compare generator output by converting fuel energy to watt equivalents.
• Cross-check published device efficiency figures from energy-over-time datasheets.

Frequently Asked Questions