Over a long period of time, many different units have been used to measure energy. These units include Calories in the US and British Thermal Unit (BTU). However, at present in the International System Units (SI) joule is the unit used to measure energy. The International System Units is the modern form of the Metric system. One calorie equals 4.187 joules. The different units of joules are kilo joule and mega joule. A kilo joule consists of 1000 joules and a mega joule consists of 1000000 joules.

When measuring electrical energy, we remember that a watt = one joule per second. In other words, one watt-second equals one joule.

Watt-seconds or using another unit of time, the Watt-hour or the Kilowatt-hour are commonly used units of energy for electricity. One kilowatt-hour ( kWh) is equal to 3 600 000 joules. (3.6 Mj)

Watt-seconds or using another unit of time, the Watt-hour or the Kilowatt-hour are commonly used units of energy for electricity. One kilowatt-hour ( kWh) is equal to 3 600 000 joules. (3.6 Mj)