How many joules are in one watt-hour?

One watt-hour (Wh) equals exactly 3,600 joules (J). A watt is one joule per second, and one hour has 3,600 seconds, so 1 Wh = 1 W × 3,600 s = 3,600 J.

How many joules are in one kilowatt-hour?

One kilowatt-hour (kWh) equals 3,600,000 joules (3.6 MJ). Since 1 kWh = 1,000 Wh and 1 Wh = 3,600 J, you get 1,000 × 3,600 = 3,600,000 J.

What is the formula to convert watt-hours to joules?

Multiply the watt-hour value by 3,600: J = Wh × 3,600. For kilowatt-hours: J = kWh × 3,600,000. Example: 5 Wh = 5 × 3,600 = 18,000 J.

What is the formula to convert joules to watt-hours?

Divide the joule value by 3,600: Wh = J / 3,600. For kilowatt-hours: kWh = J / 3,600,000. Example: 72,000 J = 72,000 / 3,600 = 20 Wh = 0.02 kWh.

When should I use watt-hours instead of joules?

Use watt-hours (or kWh) when working with electrical energy — batteries, power bills, solar panels, and EV range. Use joules when working with SI physics equations, thermal energy, or mechanical energy, where joules are the standard unit.

Watt Hours to Joules Converter

Convert watt-hours (Wh) or kilowatt-hours (kWh) to joules (J) instantly — or reverse. Formula: 1 Wh = 3,600 J.

Energy Converter

Input unit

Wh kWh

Value

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kWh

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Reference Tables

Watt-Hours (Wh)	Joules (J)	kJ

Energy Source / Item	Wh	Joules (J)

1 Wh = 3,600 J • 1 kWh = 3,600,000 J • 1 J = 0.000277 778 Wh

Summary

This tool converts energy between watt-hours (Wh) or kilowatt-hours (kWh) and joules (J). One watt-hour equals 3,600 joules because a watt is one joule per second and one hour contains 3,600 seconds — so 1 Wh = 3,600 J and 1 kWh = 3,600,000 J. Watt-hours appear on battery labels and electricity bills; joules are the SI base unit used in physics and engineering. This converter handles both directions and supports inputs from milliwatt-hours to megawatt-hours.

How it works

Choose a conversion direction: Wh/kWh to J (default) or J to Wh/kWh.
Select the input unit — Wh or kWh when converting from watt-hours, or J when converting from joules.
Type a value in the input field.
The converted result appears instantly in joules, watt-hours, and kilowatt-hours.
Click any copy button to copy a result to your clipboard.

Use cases

Convert battery capacity from Wh (consumer label) to joules for physics calculations.
Translate electricity bill kWh usage into joules for energy modeling.
Convert EV battery specs (kWh) to joules for range or efficiency math.
Cross-check solar panel output in Wh against joule-based energy budgets.
Convert lab or sensor energy readings between SI (joules) and electrical (Wh) units.
Verify energy storage system capacity for engineering reports.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu