Energy Unit – Conversion and Measurement

It is often useful to know how much energy is being changed from one form to another. For example, natural gas companies need to have a way to measure the fuel demands of their customers so they can provide enough natural gas when it is most needed.

In most scientific experiments, there is some form of energy measurement. A meter is an instrument that measures energy—such as the power and gas meters located on the sides of houses—and the standard unit of energy in the metric system is called a joule (J).

Energy can be measured in many different units. A calorie is defined as the amount of heat energy needed to raise the temperature of 2.2 pounds (1 kilogram) of water by 1.8°F (1°C). Joule conversion to calorie: 1 Joule is approximately 0.2390 calorie. Power is simply the rate at which the energy is changed.

Energy can also be measured in units called foot-pounds. One foot-pound is the amount of work done in moving an object one foot against a 1-pound force. Therefore, if a 4-pound weight is lifted 6 feet off the ground, it is using 24 foot-pounds of energy.

Horsepower

Horsepower is another measurement that describes energy. But it is a measure of power, not of energy unit itself. Power is not the same as energy. Energy is the ability to do work. Power is a measure of how quickly it is done. Mechanical power is measured in units called horse-power. James Watt, a Scottish engineer, first suggested the term when working with the newly invented steam engine. When doubtful farmers asked how many horses a steam engine could replace, this term was invented in order to make a logical comparison. Watt measured the amount of work a horse did in an eight-hour period. Many types of power are now measured in units called watts (W). Horsepower kilowatt conversion: 1 kilowatt is equal to 1.341022 horsepower.

Physical units reflect measures of distance, area, volume, height, weight, mass, force, impulse, and energy. Different types of energy are measured by different physical units: barrels or gallons for petroleum; cubic feet for natural gas; tons for coal; and kilowatt-hours for electricity. To compare different fuels, it is necessary to convert the measurements to the same units. In the United States, the unit of measure most commonly used for comparing fuels is the British Thermal Unit (Btu), which is the amount of energy required to raise the temperature of 1 pound of water 1°F. One Btu is approximately equal to the energy released in the burning of a wood match.

Measuring Energy

Energy is measured in joules, which are very small amounts of energy. A mug of hot chocolate cooling down at room temperature will release about 100,000 joules. The calorie is an old-fashioned unit often used to measure the energy contained in food. A slice of bread contains about 70 calories. One calorie equals about 4,000 joules. Power is the rate at which energy is given off or used, and it is measured in watts. The use of 1 joule of energy every second is 1 watt. A 60-watt light bulb uses 60 joules of energy every second to give off heat and light.

Btu Content of Common Types of Energy

1 barrel of crude oil (42 gallons) 5,800,000 Btu
1 gallon of gasoline 124,000 Btu
1 gallon of heating oil 139,000 Btu
1 gallon of diesel fuel 139,000 Btu
1 barrel of residual fuel oil 6,287,000 Btu
1 cubic foot of natural gas 1,026 Btu
1 gallon of propane 91,000 Btu
1 short ton of coal 20,681,000 Btu
1 kilowatt-hour of electricity 3,412 Btu