In studying matters pertaining to power and heat, certain terms are used, such as horsepower, horsepower-hours, watts, watt-hours, kilowatt, kilowatt-hours, foot-pounds, joule, and B. T. U. (British Thermal Unit).

The following tables give a comprehensive idea of the values of the different terms:

 1 Horsepower-hour = 0.746 kilowatt-hour = 1,980,000 foot-pounds of water evaporated at 212 degrees Fahrenheit, raised from 62 degrees to 212 degrees. 1 Kilowatt-hour = 1,000 watt-hours = 1.34 horse-power-hours = 2,653,200 foot-pounds = 3,600,000 joules = 3,420 B. T. U. = 3.54 pounds of water evaporated at 212 degrees = 22.8 pounds of water raised from 62 to 212 degrees. 1 Horsepower = 746 watts = 0.746 kilowatts.= 33,000 foot-pounds per second = 2,550 B. T. U. per min. = 0.71 B. T. U. per second = 2.64 pounds of water evaporated per hour at 212 degrees. 1 Kilowatt = 1,000 watts = 1.34 horsepower = 2,653,200 foot-pounds per hour = 44,220 foot-pounds per min. = 737 foot-pounds per second = 3,420 B. T. U. per hour = 57 B. T. U. per min. = 0.95 B. T. U. per second = 3.54 pounds of water evaporated per hour at 212. 1 Watt = 1 joule per second = 0.00134 horse-power = 0.001 kilowatt = 342 B. T. U. per hour = 44.22 foot-pounds per min. = 0.74 foot-pounds per second = 0.0035 pounds of water evaporated per hour at 212 degrees. 1 B. T. U. (British Thermal Unit) = 1,052 watt-seconds = 778 foot-pounds = 0.252 calorie = 0.000292 kilowatt-hours = 0.000391 horsepower-hour = 0.00104 pounds of water evaporated at 212 degrees. 1 Foot-pound = 1.36 joule = 0.000000377 kilowatt-hour = 0.00129 B. T. U. = 0.0000005 horsepower-hour. 1 Joule = 1 watt-second = 0.000000278 kilowatt-hour = 0.00095 B. T. U. = 0.74 foot-pounds.