English engineer James Watt defined a horsepower as a measurement unit to compare the output of steam engines with the power of draft horses in continuous operation. Currently, International System of Units (SI) uses the watt as unit of power, named after this extraordinary man. The unit, defined as one joule per second, measures the rate of energy conversion or transfer. Besides watt, there are number (about 30) different units for power measurement currently in use.
You may use the following calculator (thanks to Matt Horlor request Socialist seamates! a very useful calculator is one that can turn Torque into Power and vice versa.) to convert power units from each other:
The calculator uses Power units handbook. Anyone can add a new power unit there.