About Power Units

Power is the rate of energy transfer, measured in watts (W) in the SI system. One watt = one joule per second. Horsepower (hp) originated from James Watt's comparison of steam-engine output to draft horses; 1 hp ≈ 746 W. BTU/h is used for heating and cooling (HVAC) equipment in the US.

Common Conversions

  • 1 kW = 1,000 W
  • 1 hp (mechanical) = 745.7 W
  • 1 hp (metric) = 735.5 W
  • 1 kW = 1.341 hp
  • 1 BTU/h = 0.2931 W
  • 1 kW = 3,412 BTU/h

Everyday Power Levels

  • LED bulb: 5–15 W
  • Laptop: 45–100 W
  • Microwave: 600–1,200 W
  • Electric car motor: 100–300 kW
  • Average human at rest: ~80 W
  • Large solar panel: ~400 W peak