Ohm's Law and AC Power Calculator
Solve for voltage, current, resistance or power from any two known values, then work out real, apparent and reactive power for AC circuits.
Ohm's law (fill in any two)
Leave two boxes empty. If more than two are filled, clear fields until exactly two remain.
AC power
How it works
Ohm's law links voltage, current and resistance. Electrical power is voltage times current. Combining them gives six useful relationships, and the calculator picks the right one for the two values you enter.
Single-phase: kVA = V × I / 1000
Three-phase: kVA = √3 × V × I / 1000
kW = kVA × power factor kvar = √(kVA² − kW²)
Worked example
A 24 V DC load draws 2 A.
- Resistance = 24 / 2 = 12 Ω.
- Power = 24 × 2 = 48 W.
A three-phase 480 V motor draws 20 A at a power factor of 0.85. Apparent power is 1.732 × 480 × 20 / 1000 = 16.63 kVA. Real power is 16.63 × 0.85 = 14.13 kW, and reactive power is about 8.76 kvar.
Common questions
What is power factor?
It is the fraction of apparent power (kVA) that does real work (kW). Motors and transformers draw reactive current that is needed for magnetizing but does no useful work, so power factor is below 1. A lower power factor means more current for the same real power.
Does this work for DC?
Yes. For DC, use the Ohm's law panel. Power factor does not apply.
Calculations are provided for convenience and education. Verify results before relying on them for design or installation.