What is the formula for joules to watts?

Power (W) = Energy (J) / Time (s). One watt is defined as one joule per second. If you deliver 100 joules over 10 seconds, the average power is 10 watts.

How do I convert kilojoules to watts?

First multiply kilojoules by 1,000 to get joules, then divide by the time in seconds. For example, 3.6 kJ over 1 second equals 3,600 W. This calculator handles the unit conversion automatically when you select kJ.

What is the difference between instantaneous and average power?

This calculator computes average power — the total energy divided by the total time. Instantaneous power can vary throughout the period. For constant-power devices the two are equal; for variable loads the average is what this tool gives you.

Can I enter a time other than seconds?

The time field expects seconds. Convert minutes to seconds by multiplying by 60, or hours by multiplying by 3,600. For example, 5 minutes = 300 seconds.

What does the reverse calculation show?

The reverse section takes the computed watts and multiplies by the entered time to reproduce the original joules. It is a confirmation step: if the numbers match your input energy, the calculation is consistent.

Is 1 watt equal to 3,600 joules?

No. One watt equals one joule per second. The 3,600 figure comes from a watt-hour: 1 watt sustained for one hour delivers 3,600 joules (1 W × 3,600 s). Power (watts) and energy (joules) are different quantities linked by time.

Joules to Watts Calculator

Name: Joules to Watts Calculator
Availability: InStock
Author: Nham Vu

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.

Inputs

Enter energy and time to calculate average power in watts.

Energy

Time (t)

Average Power

—

watts (W)

Calculation Breakdown

Formula	W = J / s
Energy input	—
Energy in joules	—
Time (t)	—
Power (W)	—
Kilowatts (kW)	—
Milliwatts (mW)	—

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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

Select your input energy unit: joules (J), kilojoules (kJ), or megajoules (MJ).
Enter the energy value in the chosen unit.
Enter the time duration in seconds over which the energy is delivered.
Click Calculate — the tool converts energy to joules, then divides by time.
The result is displayed in watts (W), kilowatts (kW), and milliwatts (mW).
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

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Joules To Kilowatts Kilowatt Hours To Watts Joules To Horsepower

Last updated: 2026-05-23 · Reviewed by Nham Vu