Electrical Power Calculator
Calculate electrical power using P = VI, P = I²R, or P = V²/R. Enter any two of voltage, current, and resistance to find power and the remaining values.
Power (P = V × I)
600 W
Voltage
120 V
Current
5 A
Resistance
24 Ω
Three equivalent forms: P = V·I, P = I²R, and P = V²/R. Power is in watts (W).
Frequently Asked Questions
How do you calculate electrical power?
Electrical power equals voltage times current: P = V × I, measured in watts. For example, 120 V drawing 5 A consumes 120 × 5 = 600 watts.
What are the three power formulas?
Using Ohm's law you can write power three ways: P = V × I (voltage and current), P = I² × R (current and resistance), and P = V² / R (voltage and resistance). All give the same result for a resistive load.
How do I find power from current and resistance?
Use P = I² × R. Square the current and multiply by the resistance. For example, 3 A through 10 Ω dissipates 3² × 10 = 90 watts.
How do I find power from voltage and resistance?
Use P = V² / R. Square the voltage and divide by the resistance. For example, 12 V across 4 Ω dissipates 12² / 4 = 36 watts.
What is the unit of electrical power?
The SI unit of power is the watt (W), equal to one joule per second. One kilowatt (kW) is 1,000 watts.