Power Calculator — Electrical and Mechanical Power
Calculate power in watts for electrical circuits and mechanical systems. Covers P = VI, P = Fv, horsepower, and energy consumption calculations.
Power is the rate at which energy is transferred or work is done. A 100W light bulb and a 1000W microwave both use electrical energy, but the microwave does it ten times faster. That's the core idea: same energy could take different amounts of time, and power captures that time dimension.
The CalcHub power calculator handles both electrical and mechanical power in one place.
The Formulas
Electrical power:- P = V × I (voltage × current)
- P = I² × R (useful when voltage is unknown)
- P = V² / R (useful when current is unknown)
- P = W / t (work divided by time)
- P = F × v (force × velocity, for constant force)
Unit Conversions Worth Knowing
| Unit | Equivalent |
|---|---|
| 1 kilowatt (kW) | 1000 W |
| 1 horsepower (hp) | 746 W |
| 1 kWh of energy | 3,600,000 J |
| 1 BTU/hr | 0.293 W |
Electrical Examples
| Device | Typical Power |
|---|---|
| LED bulb | 8–12 W |
| Laptop charger | 45–100 W |
| Desktop computer | 200–600 W |
| Electric kettle | 1500–3000 W |
| Electric car charger | 7,000–22,000 W |
Worked Example
A motor lifts a 500 kg load vertically at 0.4 m/s. What power is required?
Force = mg = 500 × 9.81 = 4905 N
P = F × v = 4905 × 0.4 = 1962 W ≈ 2 kW
That's about 2.6 horsepower. In practice, motor efficiency is 85–95%, so the actual electrical input would be around 2.1–2.3 kW.
How do I calculate my electricity bill?
Energy consumed (kWh) = Power (kW) × Time (hours). A 2 kW heater running for 5 hours uses 10 kWh. Multiply by your rate per kWh. In most countries, rates run 10–30 cents per kWh.
What's reactive power in AC circuits?
In AC circuits, reactive components (capacitors, inductors) store and release energy each cycle without consuming it. Reactive power (VAR) is real-looking but doesn't do useful work. True power (watts) = apparent power (VA) × power factor. For resistive loads, power factor = 1.
Is watt the same as watt-hour?
No. Watt is power (rate of energy use). Watt-hour is energy (power × time). A 100W bulb left on for 10 hours uses 1000 Wh = 1 kWh of energy. The distinction matters for electricity bills and battery sizing.