How many joules are in one watt-hour?

One watt-hour (Wh) equals exactly 3,600 joules (J). This follows from the definition: 1 watt = 1 joule/second, and 1 hour = 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 joules to watt-hours?

Divide the joule value by 3,600: Wh = J / 3,600. For kilowatt-hours, divide by 3,600,000: kWh = J / 3,600,000. Example: 7,200 J = 7,200 / 3,600 = 2 Wh = 0.002 kWh.

Why do energy bills use kWh instead of joules?

Kilowatt-hours are a more practical scale for household electricity. A typical home uses millions of joules daily — which is unwieldy. 1 kWh = 3.6 MJ, so energy usage in the hundreds of kWh per month is far easier to read than billions of joules.

Is watt-hour the same as watt per hour?

No. A watt-hour (Wh) is a unit of energy (power × time). A watt per hour (W/h) would be a unit of power change rate — a different and rarely used quantity. Wh is what appears on battery labels and electricity bills.

Joules to Watt Hours Converter

Convert joules (J) to watt-hours (Wh) or kilowatt-hours (kWh) instantly. Also converts Wh and kWh back to joules. Formula: 1 J = 0.000277778 Wh.

Energy Converter

Input unit

Value

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kWh

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Reference Tables

Joules (J)	Wh	kWh

Energy Source / Event	Joules (J)	Wh

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

Summary

This tool converts energy between joules (J) and watt-hours (Wh) or kilowatt-hours (kWh). One watt-hour equals 3,600 joules because a watt is one joule per second and an hour contains 3,600 seconds. So 1 J = 1/3,600 Wh ≈ 0.000277778 Wh, and 1 Wh = 3,600 J. Watt-hours and kilowatt-hours appear on electricity bills, battery capacity specs, and solar panel output reports. The joule is the SI base unit of energy used in physics and engineering.

How it works

Choose a direction: J to Wh/kWh (default) or Wh/kWh to J.
Select the input unit — J, Wh, or kWh.
Enter a value in the input field.
Results appear instantly in watt-hours, kilowatt-hours, and joules.
Click any copy button to copy a result to your clipboard.

Use cases

Convert battery capacity from joules (physics specs) to watt-hours (consumer label).
Translate solar panel energy output from kWh to joules for engineering calculations.
Cross-check electricity bill kWh usage against joule-based energy models.
Convert kinetic or thermal energy in joules to the watt-hour units used in energy storage.
Verify EV charging energy from kWh specs to joules for range calculations.
Convert lab sensor energy readings in joules to Wh for reporting.

Frequently Asked Questions

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