Ohms Law Calculator
Calculate Voltage (V), Current (I), Resistance (R), and Power (P) for electrical circuits.
Enter any two values; the other two are calculated. Leave the rest blank.
Ohm’s Law Result
V = IR, and the power triangle behind it
Ohm's law states V = I × R — voltage equals current times resistance — and rearranges to I = V/R and R = V/I. Voltage is the electrical pressure, current the rate of flow, and resistance the opposition to it. The water analogy holds reasonably well: pressure, flow rate, and the narrowness of the pipe.
Power is the companion relationship, P = V × I, which combines with Ohm's law to giveP = I²R and P = V²/R. The I²R form is the one that matters practically: heat dissipation rises with the square of current, so doubling the current through a resistor quadruples the heat it must shed. That is why undersized wiring overheats, and why power transmission uses very high voltage and low current over distance.
Two limits. Ohm's law describes ohmic components, where resistance is constant — diodes, transistors and lamps are all non-ohmic, and their resistance changes with conditions. And in AC circuits resistance generalises to impedance, which includes capacitive and inductive effects that vary with frequency. For DC resistive circuits the simple form is exact.
Frequently asked questions
What is Ohm's Law formula?
Ohm's Law equation is V = I × R, where V is Voltage (Volts), I is Current (Amps), and R is Resistance (Ohms).
What is Ohm's law?
V = I x R: voltage equals current times resistance. Rearranged, I = V/R and R = V/I. Combined with P = V x I, the four quantities give twelve formulas, so any two known values determine the other two - which is what this calculator does.
How do I calculate electrical power?
P = V x I, or equivalently P = I^2 x R and P = V^2 / R by substituting Ohm's law. The I-squared form explains why current matters so much for heating: doubling the current through a fixed resistance quadruples the power dissipated, which is why undersized wiring overheats.
Does Ohm's law apply to everything?
No. It holds for ohmic conductors, where resistance is constant. Diodes, transistors, filament lamps and most semiconductors are non-ohmic - their resistance changes with voltage, temperature or direction of current - so a single V/I ratio does not describe them across their operating range.