How many joules are in one kilowatt-hour?

One kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules). This is derived from: 1 kW = 1,000 watts, 1 hour = 3,600 seconds, and 1 watt = 1 joule per second. So 1,000 × 3,600 = 3,600,000 J.

Why is kWh used instead of joules for electricity?

While the joule is the SI unit of energy, it is inconveniently small for household electricity. A typical home uses 30 kWh per day, which would be 108,000,000,000 millijoules — not a practical number. The kWh gives more human-scale values for billing purposes.

How do I convert kWh to megajoules?

Multiply kWh by 3.6 to get megajoules (MJ). For example, 10 kWh = 36 MJ. This is a commonly used conversion in energy policy and industrial applications.

How to Convert Kilowatt-Hours to Joules - Formula & Examples

The kWh to Joules Formula

Joules = kWh × 3,600,000

This is an exact conversion derived from fundamental definitions:

1 kilowatt = 1,000 watts = 1,000 joules per second
1 hour = 3,600 seconds
Therefore: 1 kWh = 1,000 × 3,600 = 3,600,000 joules = 3.6 MJ

Step-by-Step Examples

Example 1: Monthly Electricity Bill of 900 kWh

Calculation: 900 × 3,600,000 = 3,240,000,000 J = 3.24 GJ.
Result: 900 kWh = 3.24 gigajoules of energy.

Example 2: Charging a Phone Battery (0.01 kWh)

Calculation: 0.01 × 3,600,000 = 36,000 J = 36 kJ.
Result: Charging a smartphone takes about 36 kilojoules of energy.

Example 3: Running a 100W Light Bulb for 10 Hours (1 kWh)

Calculation: 1 × 3,600,000 = 3,600,000 J = 3.6 MJ.
Result: A 100W bulb running for 10 hours uses 3.6 megajoules.

Energy Conversion Reference

kWh	Joules	Megajoules	BTU	Calories
0.001	3,600	0.0036	3.412	860
0.01	36,000	0.036	34.12	8,598
0.1	360,000	0.36	341.2	85,984
1	3,600,000	3.6	3,412	859,845
10	36,000,000	36	34,121	8,598,452
100	360,000,000	360	341,214	85,984,523

Real-World Applications

Energy Policy and Research

Scientific papers and energy policy documents may use joules or megajoules for standardized comparisons, while utility bills use kWh. Converting between them is essential for comparing energy sources and consumption patterns.

Physics and Engineering

Physics calculations typically use joules (the SI unit), but practical energy discussions use kWh. Engineers working on power systems need to move between these units fluently.

Battery Technology

Battery capacity is sometimes expressed in watt-hours (Wh) or joules. An electric vehicle battery rated at 75 kWh stores 270 megajoules of energy, roughly equivalent to the energy in 7 liters of gasoline.

Key Insight

Remember that a kilowatt-hour is an energy unit, not a power unit. Power (watts) measures the rate of energy use, while energy (joules or kWh) measures the total amount used over time. Use our energy converter for all energy unit conversions.