Electrical Power Calculator
Calculate electrical power step by step: P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).
In short
Formula: P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values).
Power
1,150 W
- Formula
- P = V × I
- Kilowatts
- 1.15 kW
What this calculator does
Calculate electrical power step by step: P = V × I = I² × R = V² ÷ R (DC or resistive AC using RMS values). Worked example, questions and limitations included.
Use it to turn Known values, Voltage, Current, Resistance into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this electrical calculation.
Inputs and what they mean
- Known values
- — choice value.
- Voltage
- — number value.
- Current
- — number value.
- Resistance
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
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.
Worked example
230 V kettle drawing 5 A
- P = 230 × 5 = 1,150 W.
- 1,150 W ÷ 1,000 = 1.15 kW.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
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.
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.
Related tools
Calculate voltage divider step by step: Vout = Vin × R2 ÷ (R1 + R2).
Calculate resistance step by step: R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).
Calculate series resistance step by step: R_total = R1 + R2 + … + Rn.