# Electrical Power Calculator

> Calculate electrical power step by step: P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).

Page: https://freecalculator.tech/tools/electrical-power-calculator
Last reviewed: 2026-11-03

## Formula

P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).

- All three forms come from combining P = V × I with Ohm's law.
- V² ÷ R needs a resistance above zero.
- For AC loads that are not purely resistive, use the single-phase or three-phase power calculator, which includes power factor.
- P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).
- Inputs used: Known values, Voltage, Current, Resistance.

## Inputs

- Known values
- Voltage
- Current
- Resistance

## Worked example: 230 V kettle drawing 5 A

Real power of a resistive heating element.
1. P = 230 × 5 = 1,150 W.
2. 1,150 W ÷ 1,000 = 1.15 kW.

## Common questions

### Which formula should I use?

Use whichever two quantities you actually measured. All three give the same answer for a resistive load if the measurements are consistent.

### Is this the same as apparent power?

For resistive loads, yes. For motors and electronics, V × I gives apparent power in volt-amperes; multiply by power factor to get real watts.

### How do I get energy use from power?

Multiply power by running time. The energy calculator converts watts and hours into kilowatt-hours for you.

### How do I use the Electrical Power Calculator?

Enter the required values for Known values, Voltage, Current, Resistance. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Electrical Power Calculator use?

P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Electrical Power Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Resistive or DC loads only; reactive loads need power factor.
- Uses RMS values for AC; peak values give the wrong answer.
- Does not include supply losses or efficiency.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this electrical power calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-2

## Cite this page

- APA: Free Calculator. (2026, November 3). Electrical Power Calculator. https://freecalculator.tech/tools/electrical-power-calculator
- MLA: "Electrical Power Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/electrical-power-calculator.
- Link: Electrical Power Calculator — Free Calculator, https://freecalculator.tech/tools/electrical-power-calculator