Energy Converter
Energy is the capacity to do work or produce heat, and it is one of the most measured quantities in science, engineering, and everyday life. Whether you are reading an electricity bill, sizing a battery, or comparing the output of a power plant, the numbers are almost always expressed as energy.
All Energy Conversions
People convert energy units because different fields use different scales for the same physical quantity. Utilities bill in kilowatt-hours, physicists work in joules, and grid operators talk in gigawatt-hours. Converting between them lets you compare figures from a phone battery, a household meter, and a national power network on a single consistent scale.
Energy Units Explained
This category covers the joule (J) and kilojoule (kJ) from the SI system, plus the watt-hour family used in electricity: milliwatt-hour (mWh), watt-hour (Wh), kilowatt-hour (kWh), megawatt-hour (MWh), and gigawatt-hour (GWh). The joule is the SI unit of energy; one joule equals one watt of power sustained for one second. A watt-hour is the energy of one watt sustained for one hour, so 1 Wh equals 3,600 J. Each step up the watt-hour ladder multiplies by 1,000: 1,000 mWh = 1 Wh, 1,000 Wh = 1 kWh, 1,000 kWh = 1 MWh, and 1,000 MWh = 1 GWh.
How to Convert Energy Units
Convert by routing every value through the joule, the base unit. The key anchors are: 1 Wh = 3,600 J, 1 kWh = 3,600,000 J, and 1 kJ = 1,000 J. To convert, multiply the source value by its joule factor, then divide by the target's joule factor. Example: convert 2 kWh to kilojoules. First, 2 kWh × 3,600,000 J = 7,200,000 J. Then divide by 1,000 J per kJ: 7,200,000 ÷ 1,000 = 7,200 kJ. So 2 kWh = 7,200 kJ. The same method gives 1 kWh = 3.6 MJ = 3,600 kJ, and 1 Wh = 3,600 J. To go from joules back to watt-hours, simply divide by 3,600.
Common Uses
- Reading and estimating household electricity bills in kWh
- Sizing solar panels, inverters, and home battery storage
- Comparing phone, laptop, and electric-vehicle battery capacities
- Reporting power plant or grid output in MWh and GWh
- Physics and engineering calculations done in joules
- Rating appliance energy consumption over time
Accuracy Tips
Do not confuse energy with power: watts (W) measure rate, while watt-hours (Wh) measure total energy. Energy equals power multiplied by time, so a 100 W device running 10 hours uses 1,000 Wh, or 1 kWh. Watch the 1,000 versus 3,600 factors: steps within the watt-hour family scale by 1,000, but converting watt-hours to joules uses 3,600.
Frequently Asked Questions
How many joules are in a kilowatt-hour?
One kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules). This is because 1 kWh is 1,000 watts sustained for 3,600 seconds, and one watt-second equals one joule.
What is the difference between a watt and a watt-hour?
A watt measures power, the rate of energy use at an instant. A watt-hour measures total energy, equal to one watt sustained for one hour (3,600 joules). Energy equals power multiplied by time.
How do I convert kWh to kJ?
Multiply kilowatt-hours by 3,600 to get kilojoules, since 1 kWh = 3,600,000 J = 3,600 kJ. For example, 5 kWh = 18,000 kJ.
How many kWh are in a MWh and a GWh?
There are 1,000 kWh in one megawatt-hour and 1,000,000 kWh in one gigawatt-hour. Equivalently, 1 GWh = 1,000 MWh.
Why is the joule the base unit for energy?
The joule is the SI unit of energy, defined as the work done by a force of one newton moving an object one meter, equal to one watt-second. All other energy units here are defined relative to it.