definition

Energy

Energy is a physical quantity associated with the capacity to do work or transfer heat. The SI unit is the joule.

By AskToBot Editorial Team · Updated October 5, 2026

Energy is a physical quantity associated with the capacity to do work or transfer heat. The SI unit is the joule.

Simple example

A kilowatt-hour is 3.6 million joules. A 1 kW load operating for one hour uses 1 kWh of energy.

Read units together with the number. A value without its unit can be ambiguous; a ratio such as a percentage also needs its reference whole.

Use the Energy Calculator to connect the concept to a worked calculation.

Estimate electrical energy in kilowatt-hours from watts and hours.

Estimate distance from average speed and travel time.

Divide total distance by total elapsed time.

For DC circuits, multiply voltage by current: P = V × I.

Multiply power in kilowatts by actual operating hours to estimate kilowatt-hours.

Power is the rate at which energy is transferred or work is done. Its SI unit is the watt.

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