What is the formula used?

The formula is P(kW) = E(J) / (t(s) × 1000). This comes from P = E / t where energy is in joules and time is in seconds, giving watts, then dividing by 1000 converts watts to kilowatts.

E(J) / t(s) gives power in watts. Since 1 kW = 1000 W, dividing by 1000 converts watts to kilowatts. Alternatively, the formula can be written P(kW) = E(J) / (t(s) × 1000).

A joule (J) is the SI unit of energy. One joule equals one watt of power sustained for one second, or one newton-meter of mechanical work.

A kilowatt (kW) is a unit of power equal to 1000 watts. It represents the rate at which energy is transferred or converted per second.

Can I use minutes or hours instead of seconds?

This tool uses seconds as the time unit, which directly yields kilowatts. To use minutes, multiply your minute value by 60 before entering it. To use hours, multiply by 3600.

Is this the instantaneous or average power?

This calculator gives the average power over the specified time interval. Instantaneous power at any moment may differ if the energy delivery rate is not constant.

Joules to Kilowatts Calculator

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

Enter energy in joules and time in seconds to calculate average power in kilowatts using P = J / (t × 1000).

Input Parameters

Energy (J)

Time (s)

Result

Enter values and press Calculate

Formula Reference

Core Formula

P (kW) = E (J) ÷ (t (s) × 1000)

Unit Conversion

1 kW = 1000 W = 1000 J/s

Horsepower

1 kW ≈ 1.341 hp

Result copied!

Summary

Enter energy in joules and time in seconds to calculate average power in kilowatts using P = J / (t × 1000).

How it works

Enter the energy value in joules (J).
Enter the duration in seconds (s).
The calculator applies P(kW) = E(J) / (t(s) × 1000).
The primary result is displayed in kilowatts (kW).
Additional conversions to watts (W), horsepower (hp), and milliwatts (mW) are shown automatically.
Use the Reset button to clear inputs and start a new calculation.

Use cases

Calculate the average power output of a battery that delivered a measured amount of energy.
Determine the power rating required for a heating element given its energy output over time.
Convert capacitor discharge energy to an equivalent average power in kilowatts.
Estimate generator output in kilowatts from measured fuel energy over a run period.
Solve physics problems that give kinetic or potential energy and ask for average power.
Size inverters or converters based on required energy delivery and available time window.
Verify motor power ratings by comparing measured joule output to nameplate kilowatts.
Support coursework requiring SI-to-practical unit conversions in energy and power.

Frequently Asked Questions

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