Calculator
Ohm’s Law Calculator
Pick what to solve for, fill in the other two values.
What is Ohm’s Law?
Ohm’s Law describes the relationship between voltage, current and resistance in a simple circuit: V = I × R. Knowing any two of the three lets you solve for the third — this calculator handles all three directions so you can plug in whichever two values you actually have.
Frequently asked questions
What do V, I and R actually mean?
Voltage (V, in volts) is the electrical "pressure" pushing current through a circuit. Current (I, in amps) is the rate of electron flow. Resistance (R, in ohms) is how much a component opposes that flow. Ohm's Law ties them together: double the voltage across a fixed resistance and current doubles too.
How is power related?
Power (in watts) is voltage multiplied by current: P = V × I. Combined with Ohm's Law, this means power can also be written as P = I²R or P = V²/R, which is why a small increase in current can cause a much larger increase in heat dissipated by a resistor.
Why can I only solve for one value at a time?
Ohm's Law has three variables and one equation, so you need exactly two known values to solve for the third. If you only know one of V, I or R, the circuit is underdetermined and there's no unique answer without more information.
Does Ohm's Law apply to all components?
It applies well to "ohmic" components like standard resistors, where resistance stays constant regardless of voltage. It doesn't hold for non-ohmic components like diodes, transistors or light bulbs, where resistance changes with voltage or temperature.