Calculate the electrical power consumed by any device using this Electrical Power Calculator. Enter any two known values — Voltage (V), Current (I), or Resistance (R) — and get Power (P) along with the remaining unknowns. Supports both DC and AC circuits (with power factor). Results include power in watts, current, voltage, and resistance. Also try the Watt Calculator.
Power (P)
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Voltage (V)
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Current (I)
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Resistance (R)
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Power (kW)
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Electrical power is the rate at which electrical energy is transferred or consumed in a circuit, measured in watts (W). It represents how much work is done per unit time by an electric current. One watt equals one joule of energy transferred per second. See also our calculate Result, Work & Power — Work and Power.
The most common formulas are: P = V × I (power equals voltage times current), P = I² × R (power equals current squared times resistance), and P = V² / R (power equals voltage squared divided by resistance). For AC circuits, the formula becomes P = V × I × pf, where pf is the power factor.
To find the power dissipated by a resistor, use either P = I² × R if you know the current and resistance, or P = V² / R if you know the voltage across the resistor and its resistance. For example, a 10 Ω resistor carrying 2 A dissipates P = 2² × 10 = 40 W.
The power factor (pf) is a dimensionless number between 0 and 1 that represents the efficiency of power usage in an AC circuit. A power factor of 1 means all supplied power is used as real (useful) work. Values below 1 indicate reactive power losses due to inductors or capacitors in the circuit. Most household appliances have a power factor between 0.8 and 1.0. You might also find our calculate Relativistic Kinetic Energy useful.
Using the formula P = V × I, the power is P = 120 V × 10 A = 1200 W (1.2 kW). For an AC circuit with a power factor of 0.9, the real power would be P = 120 × 10 × 0.9 = 1080 W.
Watts and kilowatts are both units of electrical power. One kilowatt (kW) equals 1,000 watts. Household devices are typically rated in watts (e.g., a 60 W bulb), while larger appliances and power generation are described in kilowatts or megawatts.
You need any two of the four electrical quantities: Voltage (V), Current (I), Resistance (R), or Power (P). For example, knowing voltage and current lets you calculate power directly as P = V × I. Knowing current and resistance gives P = I² × R.
Yes. Select 'DC Circuit' for standard direct current calculations using P = V × I. Select 'AC Circuit' to include the power factor, which accounts for reactive components. For purely resistive AC loads, the power factor is 1 and results are identical to DC calculations.