What Is the Watts to Joules Calculator?
This tool converts electrical or mechanical power measured in watts (W) into energy measured in joules (J), given how long the power is applied. A watt is one joule per second, so energy is simply power multiplied by time. The calculator also shows the result in kilojoules and watt-hours for convenience.
How to Use It
Enter the power in watts and the duration in seconds, then read the energy. For example, a 100 W light bulb running for 60 seconds consumes 6,000 joules. If your time is in minutes or hours, convert it to seconds first (1 minute = 60 s, 1 hour = 3600 s).
The Formula Explained
The relationship is $$E = P \times t$$ where E is energy in joules, P is power in watts, and t is time in seconds. Because \(1\ \text{W} = 1\ \text{J/s}\), multiplying watts by seconds cancels the "per second" and leaves joules. To get watt-hours, divide joules by 3600; to get kilojoules, divide by 1000.
Worked Example
A 1,500 W heater runs for 10 minutes (600 seconds). $$\text{Energy} = 1{,}500 \times 600 = 900{,}000\ \text{joules} = 900\ \text{kJ} = 250\ \text{Wh}$$ That same energy could power a 1 W LED for 900,000 seconds (over 10 days).
FAQ
Is a joule the same as a watt? No. A watt is a rate (energy per second); a joule is an amount of energy. One watt sustained for one second equals one joule.
How do I convert joules back to watts? Divide energy by time: \(P = E \div t\). You need the duration to find power.
What about kilowatt-hours? \(1\ \text{kWh} = 3{,}600{,}000\ \text{J}\). Divide joules by 3.6 million to get kWh.
