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Electrical Power Calculator

Calculate electrical power from voltage, current, resistance, and power factor for DC and AC study scenarios.

Use calculator Open circuit simulator
Professional workflow

Convert between watts, volts, amps, and resistance for common electrical problems.

DC: P = V × I · AC real power: P = V × I × PF
  • Helps translate between volts, amps, watts, and power factor in a single focused workflow.
  • Useful for estimating load current from a known wattage before checking wire and breaker sizing.
  • Separates simple DC math from AC real-power calculations where power factor matters.

使用 P = VI 计算电功率

💡 直流电路: P = V × I

For AC loads, choose AC and enter the power factor from the nameplate or datasheet.
Use watts for real power; apparent power and VA sizing may need a separate check.
Leave one value blank to solve voltage, current, or power from the other two.

P = V × I

功率 = 电压 × 电流

Inputs to prepare
  • Voltage
  • Current
  • Power in watts
  • AC or DC mode
  • Power factor for AC loads
Worked example

Example: Find current for a 1,500 W load

Given
  • • Power = 1500 W
  • • Voltage = 120 V
Steps
  1. 1. Use I = P / V for a simple resistive load.
  2. 2. Divide 1500 by 120.
I = 12.5 A before applying any continuous-load or code adjustment.
Common use cases
  • Estimating appliance or equipment current
  • Checking exam formula answers
  • Comparing DC loads and AC loads with power factor
How to read results
  • Higher wattage at the same voltage means higher current and more conductor/loading impact.
  • A lower power factor increases current for the same real power in AC circuits.
  • Use the result as an input to wire-size, breaker, or voltage-drop checks.
Code and safety notes
  • Continuous loads, motor loads, and nonlinear loads may require code-specific multipliers or nameplate data.
  • Apparent power and real power are different in AC systems.
  • Breaker and conductor sizing must be verified using local electrical rules.

Frequently asked questions

How do I calculate watts?

For simple DC circuits, watts equal volts multiplied by amps.

Does power factor matter?

Yes. In AC circuits, real power depends on voltage, current, and power factor.

Can this help with electrician exams?

Yes. Power formulas are common in electrical exams and troubleshooting.

Are results saved?

Free accounts can save 5 calculator history items per month. Pro and Lifetime accounts can save unlimited history.