Power and Energy - Explained

POWER is the rate at which we convert or use energy. ENERGY is what we have to work with.

Power (Rate) Watt

Power is the RATE of doing work continuously, and NOT the AMOUNT of work done. The Watt is the unit of measure for electrical work done continuously. Appliances that plug into outlets are rated in Watts, such as a 100 Watt light bulb.

Think of Watts as a car's speedometer. It is the rate at which work (power) is needed or done continuously.

Energy (Amount) kWhs

Energy is the AMOUNT of work done over time. The kilowatt-hour (kWh) is the unit of measure for electrical energy (AMOUNT) consumed per hour (time). The rate of doing work (power) is multiplied by the time used to give the amount of work done: Energy = Power X Time.

The utility company charges by the kilowatt-hour for energy used.

Think of kilowatt-hours as a car's odometer. It is the rate x time. Driving at 50 mph for 1 hour is 50 miles traveled.

One 100 Watt light bulb running for 10 hour consumes 1 kWh of energy: 1 x 100 Watt bulb x 10 hours = 1,000 Watts... and 1,000 Watts / 1,000 = 1 kWh.


Enter the watts of an appliance and the time the appliance will be on. Press Calculate to see the results.

The Watt Rating, such as a 100 Watt bulb
The length of time ON
  Calculates kilowatts and kWhs
Total Watts:
Total Watts = Watts x Time
kWhs (kilowatt-hours) = kilowatts / 1,000

Multiply kWhs results times the cost per kWhs from your utility bill to see the what the cost of Watts for the hours run. Example: 1.500 kWhs x $.10 = $.15.