Electric Power Calculator
Enter voltage, current and resistance to compute electric power P = V·I = I²·R = V²/R.
Input Data
Results
At a glance:Electric power P is the rate at which electrical energy is delivered or dissipated: P = V·I, where V is voltage across and I is current through a component. Combining with Ohm's law V = I·R gives the equivalent forms P = I²·R and P = V²/R. In resistive loads power becomes heat (Joule heating). The unit is the watt (W = V·A). Enter any two of V, I, R to get P; this tool auto-selects the appropriate formula.
Formula
P = V·I
P = I²·R
P = V²/R
How to Use
- Choose a mode (voltage & current, current & resistance, or voltage & resistance).
- Enter the two known quantities.
- The calculator returns the power P.
Case Studies
Light bulb
60 W bulb at 120 V.
I = P/V = 0.5 A.
Resistance R = V²/P = 240 Ω.
FAQ
Which formula should I use?
P = V·I always works; P = I²·R and P = V²/R require knowing R (i.e. a resistive load obeying Ohm's law). This tool picks the right one from what you enter.
Why does P = I²·R matter for wiring?
Power lost as heat in a wire is I²·R, so higher current causes disproportionately more heating — the basis for using thick wires and high-voltage transmission.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.