Electrical Power Calculator

How to solve an electrical power problem

Pick your two known quantities — any pair of voltage, current, resistance, or power.
Enter their values in volts, amps, ohms, and watts.
Press Calculate. The codex solves the other two and shows the formulas used.
Check the units — watts of power tell you how fast energy is used (watt-hours tell you the total).

What is the electrical power formula?

Power P (in watts) = voltage V (in volts) × current I (in amps). Combined with Ohm’s law (V = I × R), you also get P = I² × R and P = V² / R.

How do you find power with only voltage and resistance?

Use P = V² / R: square the voltage and divide by the resistance in ohms. For example, 120 volts across 25 ohms gives 120² / 25 = 576 watts.

What is Ohm’s law?

Ohm’s law states that voltage equals current times resistance (V = I × R). It links the three core quantities of a simple electric circuit.

What are the units for power, voltage, current, and resistance?

Power is measured in watts (W), voltage in volts (V), current in amperes or amps (A), and resistance in ohms (Ω).

How much power does a 120-volt, 2-amp device use?

Multiply voltage by current: 120 × 2 = 240 watts. Its resistance is 120 / 2 = 60 ohms.

You’re here

Enter any two of V, I, R, P — solve all four with Ohm's law.

This tool is free, with no account and no ads. If it saved you some time, consider supporting the indie dev behind it.