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Convert between watts, horsepower, BTU/hr, and more. Includes mechanical and metric hp.
Power is the rate at which energy is transferred or converted, measured in watts (W). One watt equals one joule per second. Common units include kilowatts, horsepower, and BTU per hour.
| Description | kW | hp | BTU/hr |
|---|---|---|---|
| LED light bulb | 0.01 | 0.013 | 34 |
| Hair dryer | 1.5 | 2.0 | 5,118 |
| Window AC unit | 1.0 | 1.3 | 3,412 |
| Electric car motor | 150 | 201 | 511,821 |
| Sports car engine | 350 | 469 | 1,194,249 |
| Wind turbine (large) | 3,000 | 4,023 | 10,236,420 |
Divide watts by 745.7 for mechanical hp, or by 735.5 for metric hp (PS).
hp = W ÷ 745.7
Multiply kilowatts by 3,412.14 to get BTU per hour.
BTU/hr = kW × 3,412.14
1 watt = 1 joule per second. Power is the rate of energy transfer or work done.
1 W = 1 J/s
Formula
P (W) = E (J) ÷ t (s) | 1 hp = 745.7 W | 1 kW = 3,412 BTU/hrP = Power in watts (W) — rate of energy transfer
E = Energy in joules (J)
t = Time in seconds (s)
hp = Mechanical horsepower — historically defined as 550 ft·lbf/s
Worked Example
Convert 5 horsepower to kilowatts
Did you know? James Watt invented the term 'horsepower' in the 1780s to market steam engines — he calculated one horse could turn a mill wheel 144 times per hour, pulling with 180 lbf, giving 32,572 ft·lbf/min, which he rounded up to 33,000 ft·lbf/min (745.7 W).
Sources
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