Power Calculator

Calculate electrical power in watts from voltage and current. See the P = V x I formula with a worked volts-and-amps example.

Calculator inputs

  • Voltage (V)
  • Current (A)

Formula

P = V * I

How this calculator works

Enter voltage in volts and current in amps to calculate electrical power in watts. This calculator uses the direct-current and resistive-load relationship P = V x I.

Worked example

A 120-volt device drawing 10 amps uses 1,200 watts because 120 x 10 = 1,200.

Common mistakes

  • Mixing milliamps and amps without converting first. Divide milliamps by 1,000 to get amps.
  • Treating the basic P = V x I result as an exact AC power measurement when power factor matters.
  • Entering kilovolts or kiloamps as though they were volts or amps.

Frequently asked questions

How do you calculate watts from volts and amps?

Multiply volts by amps. The formula is P = V x I, where P is power in watts, V is voltage in volts, and I is current in amps.

How many watts is 120 volts at 10 amps?

The result is 1,200 watts: 120 volts multiplied by 10 amps.

Does power factor affect this calculation?

Yes for many AC loads. This calculator uses P = V x I and does not apply a power-factor adjustment, so use the result as apparent input power unless the load is resistive or power factor is 1.

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