Electric Power Calculator
Calculate electrical power in watts from voltage and current, plus resistance and the power formulas P=VI, P=I squared R and P=V squared over R.
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Calculate electrical power in watts from voltage and current.
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Calculate electrical power
Electrical power is the rate at which electrical energy is used or produced, measured in watts. The most direct formula is power equals voltage multiplied by current, so a twelve-volt supply delivering two amps provides twenty-four watts. This calculator computes power from voltage and current, and also derives the resistance using Ohm's law and expresses the result in kilowatts. The three classic power formulas, voltage times current, current squared times resistance, and voltage squared divided by resistance, all give the same answer.
Knowing power consumption is essential for sizing components, wiring and power supplies safely.
Where power calculations are used
Students meet electrical power throughout physics and electronics, and it is a practical calculation for anyone working with circuits, appliances or solar systems. Power determines how much energy a device uses over time, which in turn drives electricity costs and the heat a component must dissipate. Undersizing wiring or a supply for the power involved is a common cause of failures and hazards.
The watt is one joule per second, linking power to energy and time. Multiply power by hours of use to get energy in watt-hours. All calculation happens locally in your browser.
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Frequently Asked Questions
What is the electric power formula?
The basic formula is power equals voltage times current. Equivalent forms are current squared times resistance, and voltage squared divided by resistance.
What unit is electrical power measured in?
Watts, where one watt equals one joule of energy per second. Larger values are often given in kilowatts, which are thousands of watts.
How do I find resistance from this?
Using Ohm\'s law, resistance equals voltage divided by current, which the calculator shows alongside the power.
How does power relate to energy cost?
Energy used equals power times time. Multiplying watts by hours gives watt-hours, which electricity is billed by, usually in kilowatt-hours.
Why does component sizing depend on power?
Power determines heat and current, so wires, supplies and components must be rated for the power involved to operate safely.
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How to Use
Enter voltage and current to calculate power and resistance.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.