EngineeringFormulaPower (P)
Power is the rate at which work is done or energy is transferred, per unit time.
Mechanically, P = T × ω relates power to torque and rotational speed. Electrically, P = VI relates it to voltage and current, with real, reactive, and apparent power diverging once a circuit's power factor departs from 1. Base SI unit is the watt (W); mechanical work commonly uses horsepower (hp) instead.
A useful sanity check: two machines can produce identical power from very different torque-and-speed combinations - a high-torque, low-RPM motor and a low-torque, high-RPM motor can deliver the same watts. That's exactly why gearboxes exist: to trade torque for speed (or the reverse) while power stays roughly constant, minus mechanical losses.
Choose the calculator based on context: Horsepower or Torque for rotating shafts, Electrical Power for DC or simple electrical loads, Three-Phase Power for line-to-line AC equipment, and Pump Hydraulic Power for flow against head.
Typical Power by Context
| Context | Power |
|---|---|
| Sustained human physical output | 75–100 W |
| Household microwave | 1–1.5 kW |
| Passenger car engine | 75–150 kW (100–200 hp) |
| Large utility wind turbine | 2–5 MW |
Used In These Calculators
Frequently Asked Questions
What's the difference between power and energy?
Power is a rate (how fast energy is used or transferred, in watts); energy is the total amount transferred over time (in joules, or kWh for electricity billing). A 1 kW heater run for 1 hour uses 1 kWh of energy - the power rating alone doesn't tell you the total energy without also knowing the duration.
Why do electric motors have both a horsepower and an amperage rating?
Horsepower (or watts) describes the mechanical power the motor delivers at its shaft; amperage describes the electrical current it draws to produce that power. The two are linked by P = VI and the motor's efficiency, but they answer different questions - one is about output, the other is about what wiring and breaker size the motor needs.
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