What are the power formulas?

P = V × I (voltage times current), P = I² × R (current squared times resistance), and P = V² / R (voltage squared divided by resistance). All three give power in watts.

Which formula should I use?

Use whichever two quantities you already know. The calculator offers all three combinations so you never have to convert first.

How do I find watts from volts and amps?

Multiply them: P = V × I. A 12 V supply delivering 2 A gives 12 × 2 = 24 watts. Choose the volts-and-amps mode for this.

How do I calculate power from current and resistance?

Use P = I² × R. A 2 A current through a 3 Ω resistor dissipates 2² × 3 = 12 watts of power, all turned into heat in the resistor.

How do I calculate power from voltage and resistance?

Use P = V² ÷ R. A 12 V drop across a 4 Ω resistor gives 12² ÷ 4 = 144 ÷ 4 = 36 watts.

Why are there three formulas for the same thing?

They are all the same law combined with Ohm's law (V = I × R). Substituting V or I lets you compute power from whichever pair of quantities you happen to know.

Power (Watts) Calculator

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No — every calculation runs locally in your browser, with no network requests.

Electrical power (watts) calculator

Electrical power — the rate at which energy is used or dissipated, measured in watts — can be found three equivalent ways depending on which quantities you know. This calculator lets you pick the pair you have (voltage, current or resistance) and returns the power instantly, so you never have to rearrange the formula yourself. Handy for circuit design, sizing components and electronics homework.

How it works

All three formulas come from the power law combined with Ohm’s law (V = I × R):

P = V × I        (voltage × current)
P = I² × R       (current squared × resistance)
P = V² ÷ R       (voltage squared ÷ resistance)

Choose the mode matching your known values, enter the two numbers, and the watts appear below.

Example

A circuit with 12 V and 2 A:

P = V × I = 12 × 2 = 24 W

The same power from current and resistance, or voltage and resistance:

Known values	Formula	Power
12 V, 2 A	V × I	24 W
2 A, 3 Ω	I² × R	12 W
12 V, 4 Ω	V² ÷ R	36 W

Every calculation runs locally in your browser, with no network requests.