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Electrical Power calculator
Calculate electrical power and energy from voltage, current or resistance, and estimate energy use in kilowatt-hours.
Electrical Power calculatorElectrical Power
P = VI = I²R = V²/R · Full Power Analysis
P = V × I | P = I²R | P = V²/R | Energy: E = P × t
Electrical power is the rate at which a device consumes or delivers energy, and it is fixed by two numbers: the voltage across it and the current through it. This calculator solves P = V × I in any direction, for appliances, circuits and power supplies.
How to use this calculator
- Enter any two of: power (watts), voltage (volts), current (amps).
- Press calculate to see the third value.
Watts are what you pay for, amps are what wires feel
Bills are charged on energy, which grows from watts over time, while cables, fuses and breakers care about amps. A device can be cheap to run and still trip a breaker if it draws its watts at low voltage and high current, which is why both figures belong in any real installation decision.
Frequently asked questions
What is the electrical power formula?
P = V × I. With resistance known, also P = I²R or P = V²/R, all equivalent through Ohm's law.
How many watts does a typical appliance use?
Rough guides: an LED bulb about 10 W, a laptop 50 W, a microwave 1,000 W, an electric heater 2,000 W. The rating plate on the device is the figure to trust.
How do I find the current a device draws?
Divide its watts by the supply voltage. A 2,300 W heater on a 230 V supply draws 10 A.