Power is defined as the rate at which energy is used or consumed. The value is used to characterize energy use in a vast array of systems, from electrical engines to everyday household appliances. There are many different units of power, but the international system (SI) of units uses the watt. Two less known units of power are horsepower and the British thermal unit (BTU).

Converting between two older, nonstandard units may seem strange; however, many specific industries use these units. For example, the power of a boiler is often expressed in BTU, and car engines' power is often expressed in horsepower. To convert BTU per hour to horsepower use the following equation:

Power (Horsepower) = Power (BTU per hour) x 2,545.