
Energy Measurement
Although energy can exist in many different forms, it can be measured and compared along a single axis because it can be converted between forms. Measurement of the familiar forms of energy involves measuring quantities of mechanical force, weight, distance, temperature, electric charge and current, and/or time.
unit  defnition  equivalent units  

joules  kWh  BTUs  
SI* unit of energy  joule  Force of 1 newton over distance of 1 meter; Watt second 
1  2.777*10^{7}  9.481*10^{4} 
Commonly unit of electrical energy  kWh (kilowatt hour)  Power of 1,000 watts for 1 hour  3,600,000  1  3,413 
Common English units of thermal energy or fuel equivalents  BTU (British Thermal Unit)  Temperature increase of 1 degree Fahrenheit in 1 pound of water at 1 atmosphere  1,055  2.931*10^{4}  1 
therm  100,000 BTUs  1.055*10^{8}  29.3  100,000  
CCF (Hundred Cubic Feet)  1 hundred cubic feet of natural gas at standard pressure  103,100  
GGE (Gasoline Gallon Equivalent)  Energy content of 1 liquid gallon of gasoline  1.2*10^{8}  33.4  114,113  
Other units of energy  erg  Force of 1 dyne over distance of 1 centimeter  10^{7}  
(kilogram) calorie  Temperature increase of 1 degree Celseus in 1 kilogram of water at 1 atmosphere  4.19 
* The International System of Units (SI) is the modern form of the metric system and has units of measurement defined in terms of seven base units and numerous derived units. Accordingly, the Joule is a derived unit defined in terms of the base units of force (newton) and distance (meter).