Ohms Law Calculator
Solve Ohm's Law for voltage, current, resistance or power. Given any two values, the calculator returns the other two.
How to use the Ohms Law Calculator
- Enter your inputs into the Ohms Law Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
Ohm's Law and the power equation
V = I × R · · · P = V × I = I² × R = V² / R
V is voltage (volts), I is current (amps), R is resistance (ohms), P is power (watts). The power equations follow directly from Ohm's Law by substitution.
Worked example
A 12 V battery connected through a 4 Ω resistor: I = V/R = 12/4 = 3 A. Power dissipated = V × I = 12 × 3 = 36 W. Or equivalently I²R = 9 × 4 = 36 W.
Frequently asked questions
Does Ohm's Law apply to AC circuits?
For purely resistive AC circuits, yes (using RMS values). For circuits with inductors or capacitors, impedance Z replaces R: V = I × Z, and Z is complex (resistance + reactance).
What is the difference between voltage and current?
Voltage is electrical potential difference — the "pressure" pushing current. Current is the flow of charge — the actual amount of electrons moving. Voltage causes current to flow through resistance.
Why does power equal I²R?
Combining P = V×I and V = I×R: P = (I×R) × I = I²R. The squared term means doubling current quadruples power dissipated (and heat generated).