Power converter

Six units of power at once, including both horsepowers. Mechanical horsepower is about 746 watts and metric horsepower about 735 — roughly a 1.4 percent difference, which is why the same car is quoted at different numbers in different markets.

Power is energy per unit time, and confusing the two is the commonest mistake in this area: a kilowatt is a rate, a kilowatt hour is an amount. A 2 kW heater running for three hours uses 6 kWh. The two horsepowers exist for a dull historical reason — mechanical horsepower was defined as 550 foot-pounds per second and metric horsepower as 75 kilogram-metres per second, and neither side adopted the other. Air conditioning is rated in BTU per hour, which is also power despite sounding like energy; 12,000 BTU/h is one "ton" of cooling, about 3.5 kW.