Power

Since power is a measure of the rate at which work is done, the underlying units are those of work or energy, and that section should be looked at for explanations concerning the calorie and Btu. In this section the (IT) values have been used.

In this section it is the horsepower which provides confusion. Just like the calorie, it can take 5 different values, and these are identified as necessary by the addition of (boiler), (electric), (metric), (UK) and (water). Unlike the calorie (whose 5 values are reasonably close to each other), the horsepower has 4 which are close and 1 (boiler) which is considerably different - it is about 13 times bigger than the others - but it seems to be very little used.

The S I unit of power is the watt. To change any of these other units of energy or work into their equivalent values in watts use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.

Btu/hour x 0.293 071

Btu/minute x 17.584 267

Btu/second x 1055.056

calories/hour x 0.001 163 #

calories/minute x 0.069 78 #

calories/second x 4.1868 #

ft lb-force/minute x 0.022 597

ft lb-force/second x 1.355 82

gigawatts [GW] x 1 000 000 000

horsepower (electric) x 746 #

horsepower (metric) x 735.499

watts [W] 1

joules/hour divide by 3600 #

joules/minute divide by 60 #

joules/second 1

kilocalories/hour x 1.163

kilocalories/minute x 69.78

kg-force metres/hour x 0.002 724

kg-force metres/minute x 0.163 444

kilowatts [kW] x 1000 #

megawatts [MW] x 1 000 000 #

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DICTIONARY OF UNITS

Power