Power Converter

Power is the rate of doing work or using energy, measured in watts (W). One watt is one joule per second, so power tells you how fast energy flows, not how much of it there is.

Key relationships:

• 1 kW = 1,000 W
• 1 MW = 1,000,000 W
• 1 HP (mechanical) = 745.7 W
• 1 BTU/h = 0.29307 W

Common references:

• An LED bulb: about 10 W
• A microwave: about 1,000 W (1 kW)
• A 200 HP car engine: about 149 kW
• A window AC unit: rated in BTU/h, often 8,000–12,000

Horsepower carries a fun bit of history. James Watt coined it in the 1770s to sell his steam engines, pitching their output against the draft horses they replaced. He estimated what a horse could sustain and rounded it into a unit, which is why “horsepower” still sells engines and lawn mowers today even though it’s a marketing relic.

One wrinkle worth knowing: horsepower isn’t a single value. Mechanical horsepower is 745.7 W, but metric horsepower (about 735.5 W, the “PS” or “CV” on European cars) and electrical horsepower (746 W) differ slightly, so figures don’t always line up exactly. And note that air conditioners are rated in BTU per hour, which is a power despite the BTU looking like an energy unit.