Motor Power Converter

Motor power conversion factors.

Base conversions:

• 1 HP (mechanical) = 745.7 watts = 0.7457 kW
• 1 kW = 1.341 HP = 1,000 watts
• 1 HP = 2,544.43 BTU/hr
• 1 kW = 3,412.14 BTU/hr

Common motor sizes:

• Small fan: 1/4 HP (186 W)
• Garage door opener: 1/2 HP (373 W)
• Power tools: 1-3 HP (746-2,237 W)
• Car engine: 150-300 HP (112-224 kW)
• Electric car: 200-400 HP (149-298 kW)
• Diesel truck: 300-600 HP (224-447 kW)

Types of horsepower:

• Mechanical/Imperial HP: 745.7 W (used for engines)
• Metric HP (PS): 735.5 W (used in Europe)
• Electrical HP: 746 W (used for electric motors)

Those three flavors of horsepower exist because the unit was adopted by different industries, and the gaps are small but real: a “150 PS” European car works out to about 148 mechanical hp, which is why the same engine can wear two different numbers in two markets.

A more important distinction for electric motors is input versus output power. The watts a motor pulls from the supply aren’t all delivered to the shaft, because no motor is perfectly efficient, so a unit rated “1 kW output” draws somewhat more than 1 kW from the wall, the difference lost as heat. It’s also worth checking whether a rating is continuous or peak. Many motors can briefly produce far more than they can sustain, and mistaking the short-term peak for the continuous rating is a common way to burn out an undersized motor.