Just as there are many forms of energy, there are different ways to measure and quantify these forms. In science, work and energy are commonly measured in joules. One joule is the amount of energy it takes to lift an object that weighs one Newton a one-meter distance. A Newton is the metric unit for weight and is comparable to the weight of an apple. (1 lb = 4.45 Newtons)
In our everyday lives, other energy measurements are more familiar to us than joules. Some of these units of measurement include Btus, calories, and kilowatt-hours. Definitions of these and other units are found below.
It might seem confusing to have so many different units of measurement for energy. The good news is that one unit can be converted into another. (See Energy Conversion and Resource Tables).
British thermal unit – (abbrev. Btu)
Calorie (abbrev. cal; pl. calories; also small calorie):
Foot-pound (abbrev. ft-lb; pl. foot-pounds):
Joule – (abbrev. J; pl. Joules):
Kilowatt-hour (abbrev. kWh; pl. Kilowatt-hours):
Therm – (pl. Therms):
Power is defined as the rate at which energy is transferred or converted per unit of time. It is also the rate at which work is done. Some units of measure for power include horsepower and Watt.
One way to help distinguish between energy and power is to think of two people each eating an apple pie. One person eats their pie faster than the other. They both ate the same amount of pie (they consumed the same amount of energy), and one just ate the pie at a faster rate (the faster one was a power eater!).
Like units of energy, units of power can be converted to another. (See Energy Conversion and Resource Tables).
Horsepower (abbrev. hp):
Watt (abbrev. W; pl. Watts):