Ohm's Law & Electrical Power Calculator
Solve voltage ($V$), current ($I$), resistance ($R$), and power ($P$) for DC circuits as well as single-phase and three-phase AC systems.
Enter any 2 known values and leave the other 2 blank to solve them:
What does the Ohm's Law & Power Calculator do?
The Herramix Ohm's Law & Electrical Power Calculator solves both direct-current (DC) circuits and single-phase or three-phase alternating-current (AC) power triangles. In the DC tab, simply enter any two known variables among voltage ($V$), current ($I$), resistance ($R$), and power ($P$) to compute the remaining two automatically.
Switch to the AC Power tab to compute real active power ($\text{kW}$), apparent power ($\text{kVA}$), reactive power ($\text{kVAr}$), and equivalent horsepower ($\text{HP}$) from line voltage, line current, and power factor ($\cos\varphi$).
Usage example
Scenario: A balanced 3-phase industrial motor running at 400 V draws 25 A with a power factor of $\cos\varphi = 0.85$.
Result: Active power $P = 14.72\text{ kW}$ · Apparent power $S = 17.32\text{ kVA}$ · Reactive power $Q = 9.12\text{ kVAr}$.
Frequently Asked Questions
What are the main Ohm's Law formulas?
Ohm's Law states that $V = I \times R$. Combined with Watt's Law ($P = V \times I$), you can solve any parameter: $I = V / R$, $R = V^2 / P$, $P = I^2 \times R$, and $V = \sqrt{P \times R}$.
How do you calculate power in a three-phase AC circuit?
For a balanced three-phase load, multiply by $\sqrt{3} \approx 1.73205$: active power is $P = \sqrt{3} \times V \times I \times \cos\varphi$, apparent power is $S = \sqrt{3} \times V \times I$, and reactive power is $Q = \sqrt{3} \times V \times I \times \sin\varphi$.
What is power factor ($\cos\varphi$)?
Power factor is the cosine of the phase angle between voltage and current waveforms. It represents the fraction of apparent power ($\text{kVA}$) that performs useful work ($\text{kW}$).