Power Calculator

What this calculator does

The Power Calculator provides fast estimates using standard electrical relationships. Enter Voltage (V), Current (I), Resistance (R) to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Voltage (V): Voltage in Volts.
  • Current (I): Current in Amperes.
  • Resistance (R): Resistance in Ohms (Ω).
  • Power (P): Power value as labeled (W, kW, VA, or kVA).

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units. For AC calculations, power factor and phase selection adjust real power to match typical loads.

Formulas used

  • P = V x I
  • P = I²R = V²/R

Units: V in volts (V) I in amperes (A) R in ohms (ohm) P in watts (W)

⚡

Power Calculator

Calculate electrical power (watts)

Enter any two values to calculate the others:

V
A
Ω
W
Result
Enter 2 values

Power Formulas

BasicP = V × I
With RP = I²R = V²/R

Units

1 kW = 1000 W
1 MW = 1,000,000 W
1 HP ≈ 746 W
1 kWh = 1 kW for 1 hour

Related

Ohm's LawWatts to AmpskW to Amps

Step-by-step example

Scenario: Calculate power for 12V circuit drawing 3A.

Formula: P = V x I

  1. P = 12 x 3
  2. P = 36 Watts

Result: 36 Watts

Use cases

  • Estimate electrical power from voltage and current inputs.
  • Check power against equipment ratings.
  • Compare power under different operating conditions.
  • Create quick sanity checks during troubleshooting.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Power Calculator converts between electrical units using your inputs. It is designed for quick checks and planning. Results are idealized and intended for estimation. Use it to compare scenarios and validate hand calculations. Confirm results with measurements when accuracy matters. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

The calculator applies standard electrical formulas based on the inputs. Typical relationships include P = V x I and related variations. AC options include power factor adjustments. Three-phase options use the sqrt(3) factor when required. Use consistent units to avoid scaling errors. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Use nameplate or measured values when possible. Confirm whether voltage is line-to-line or line-to-neutral. Use RMS values for AC current and voltage. Choose a realistic power factor for inductive loads. Document assumptions for later review. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Yes when the calculator includes system type options. DC assumes power factor of 1.0. AC uses RMS values and PF adjustments. Harmonics and non-sinusoidal waveforms can change results. Use the tool for estimates and planning only. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Results are accurate for ideal conditions and correct inputs. Voltage tolerance and measurement error can shift outcomes. Power factor can change with load. Use measured values for better accuracy. Treat the output as an estimate. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

No. This calculator is for education and planning only. Final wiring and breaker sizing must follow local codes. Manufacturer specs should be verified. Consult a licensed electrician for installations. Use this tool to support early estimates only. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.