The international standard unit of energy is the joule. Any amount of energy can be expressed in joules but sometimes it is helpful to use different units depending on the amount of energy, its origin, or its use.
Joule - The energy it takes to accelerate a one-kilogram mass at the rate of one meter per second over a distance of one meter.
Kilowatt-hour - Enough energy to keep a 100-watt light bulb going for 10 hours. An electric bill lists energy use in kilowatt-hours.
1 kWh = 3,600,000 joules
Calorie - The energy required to raise the temperature of one gram of water by one degree Fahrenheit. 1 cal = 4.2 joules. The energy content of food is measured in kilocalories (C) although they are usually called calories too.
1 food Calorie = 1000 cal.
Btu - British thermal unit. One Btu is the energy required to raise the temperature of one pound of water by one degree Fahrenheit.
1 kilowatt-hour = 3,411 Btu.
1 Btu = 1,055.4 joules.
Therm - 100,000 Btu. One therm is the energy in 97 cubic feet of natural gas. A household gas bill is often listed in therms.
Barrel - Oil is measured by the barrel, which is 42 gallons. Burning this oil would release about six million Btu.
Oil Tanker - A typical oil tanker transports about three million barrels of oil. There are currently more than 2,600 tankers on the world's oceans and waterways.
Ton - Coal is measured by the ton, which is 2000 lb. The energy in one ton of coal is equivalent to about four barrels of oil.
Coal Train - An average coal train pulls about 100 cars, each of which contains about 100 tons of coal. A typical coal-fired electric power plant needs deliveries from about four coal trains every day.
Quad - One quadrillion (1015 or 1,000,000,000,000,000) Btu. You must burn 170 million barrels of oil or about 40 million tons of coal to get a quad. Energy use in the United States is 60 to 70 quads each year.
How many joules in:
• one therm?
• one barrel of oil?
• one ton of coal
• one quad
• one coal
• a candy bar
• a typical oil