Power Calculator

Calculate electrical power from voltage and current, and resistance from the same two values. Formula, worked example and typical values.

Voltage 230 V, current 5 A gives

1,150 W

Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.

Open in the calculator with these values

Formula

P = V × I R = V / I

Worked example

Input	Value
Voltage	230 V
Current	5 A

P = V × I = 230 × 5 = 1,150 W
R = V / I = 46 Ω

Typical values

Current (A)	Power (W)
0.5	115
1	230
2	460
5	1,150
10	2,300
20	4,600

Other inputs are the same as in the worked example above.

Assumptions

Steady DC or purely resistive AC load
AC values are RMS

For reactive loads include power factor (watts to amps).

Frequently asked questions

How is Power calculated?

P = V × I; R = V / I. Worked example: Voltage 230 V, current 5 A gives 1,150 W.

What do I need to enter?

Enter voltage and current. Change the unit of a value with its selector and the result stays the same.

Does this work for AC circuits?

Only for resistive loads, using RMS values, where the power factor is 1. A load with reactance needs impedance and phase angle, and the power depends on the power factor; use the AC Ohm's law (phasors) calculator in Elecmetric, which takes magnitude and angle for voltage, current and impedance and returns the power triangle.

How accurate are the results?

Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.

Next steps in a design: Ohm's Law Volts to Amps Ohm's Law (V, I, R, P)
Also see: Volts to Watts
Formula guides: Ohm’s Law Formulas and Power Wheel AC Circuit Formulas: Reactance and Impedance
All 78 conversions Power from Voltage and Current in Elecmetric