Power Converter

What is power?

Power is the rate at which energy is transferred or work is done. In plain terms, it answers the question "how fast?" — how fast an engine turns fuel into motion, how fast a heater moves heat into a room, or how fast a light bulb consumes electricity. The watt (W) is the SI (metric) unit of power, named after Scottish engineer James Watt, whose improvements to the steam engine helped launch the Industrial Revolution. One watt equals one joule of energy per second (1 W = 1 J/s).

Why so many power units?

Different industries grew up with different customary units before the watt became the international standard. Mechanics in the US still quote engine output in horsepower, HVAC technicians rate air conditioners in BTU per hour, and physicists working with rotating shafts use foot-pound per second. Globally, the watt and its multiples (kilowatt, megawatt) dominate grids, solar panels, and batteries. A good power converter lets you move between all of these without memorizing factors.

The base-unit method

This converter uses a two-step "base-unit" approach. Every value is first converted into watts (the base unit), then from watts into your chosen target unit. Because the intermediate step is always the same, the math is simple multiplication and division and the result is accurate to six decimal places. For example, to convert kilowatts to mechanical horsepower: 1 kW = 1000 W, and 1 mechanical hp = 745.6999 W, so 1 kW = 1000 ÷ 745.6999 = 1.34102 hp.

Key conversion factors

• 1 watt = 1 J/s (the definition)
• 1 kilowatt = 1000 W
• 1 megawatt = 1,000,000 W
• 1 mechanical horsepower = 745.6999 W (≈ 0.7457 kW)
• 1 metric horsepower (PS) = 735.49875 W
• 1 BTU/hour = 0.29307107 W
• 1 foot-pound/second = 1.35581795 W (550 ft·lb/s = 1 hp)

Mechanical vs metric horsepower

A common source of confusion is that "horsepower" is not a single number. The mechanical (or imperial) horsepower — the one used for US car and motor specs — equals 550 foot-pounds per second, or 745.6999 W. The metric horsepower (often written PS in German or CV in French) equals 75 kilogram-force meters per second, or 735.49875 W. The two differ by about 1.4%. If you mix them up on a datasheet, your calculated motor size will be off. Always check which "hp" a spec means; our tool keeps both and labels them clearly.

Real-world examples

Imagine you buy a 1.5-ton air conditioner rated at 18,000 BTU/hour. Divide by 3412.14 (BTU/h per kW) and you get about 5.28 kW of cooling power. Or suppose a European car advertises 150 PS; multiply by 735.49875 to get 110,324 W, or about 147.9 mechanical hp. A small drone motor might be rated in watts (say 800 W); that is 1.073 mechanical hp. These everyday switches between systems are exactly what this tool handles instantly.

Common mistakes

The biggest error is treating BTU and BTU/hour as the same thing. BTU is a unit of energy; BTU/hour is a unit of power. HVAC equipment is almost always rated in BTU/hour, so make sure you use the per-hour unit here. The second mistake is forgetting that "horsepower" can mean mechanical or metric — verify before converting. The third is rounding too early: 1 kW is 1.3410 hp, not 1.34, and at large scales that rounding drifts.

Frequently asked questions