ElectraKit
Electrical fundamentals

Ohm’s Law and Power Calculator

Solve Ohm’s law values, or convert single-phase and balanced three-phase line current, kW, kVA, kvar, and power factor.

Electrical values

Choose a calculation

V
A
Calculated results
1,200W
Voltage120 V
Current10 A
Resistance12 Ω

DC or purely resistive circuit relationship.

Reference onlyOhm’s law mode assumes a DC or purely resistive circuit. AC results use RMS line values and assume a balanced three-phase load when selected. They do not account for harmonics, unbalance, or equipment-specific conditions.

About this calculator

Use Ohm’s law mode to enter any two of voltage, current, resistance, and power. The calculator solves the remaining values for a DC or purely resistive circuit.

For AC loads, choose single-phase or balanced three-phase mode, then enter line voltage, power factor, and one known value: line current, kVA, or kW. The calculator derives line current, kW, kVA, and kvar.

Method and assumptions

Ohm’s law uses V = I × R and P = V × I, with equivalent forms used to solve each supported pair of known values. AC apparent power is V × I for single-phase and √3 × V × I for balanced three-phase systems. Real power is apparent power multiplied by power factor; reactive power is derived from the power triangle and reported as a magnitude.

When kVA is known, line current is kVA × 1,000 divided by line voltage and the phase factor. When kW is known, the calculator first derives kVA from power factor, then calculates line current. AC inputs are RMS line values. Three-phase calculations assume balanced phase loading and line-to-line voltage. The results do not account for harmonics, unbalance, or non-sinusoidal waveforms.

FAQs

Can I use Ohm’s law mode for AC circuits?

Use it for DC circuits or loads that behave as purely resistive. For AC power with a power factor, choose the single-phase or three-phase mode.

Which voltage should I enter for three-phase power?

Enter line-to-line RMS voltage and line current. The three-phase calculation assumes a balanced load.

Can I solve for line current from kW or kVA?

Yes. In AC mode, choose line current, apparent power (kVA), or real power (kW) as the known input. Enter line voltage and power factor; the calculator derives current and the remaining power quantities.

What do kW, kVA, and kvar mean?

kW is real power, kVA is apparent power, and kvar is reactive power. The calculator derives them from line voltage, one known current or power quantity, phase, and power factor. Reactive power is shown as a magnitude; the result does not indicate leading or lagging power factor.

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Sources

  • Ohm’s law and the power relationships for DC and purely resistive circuits.
  • Single-phase and balanced three-phase RMS power relationships.