Ohm's Law Calculator
Enter any two of voltage, current, resistance or power — the calculator solves for the other two using Ohm's Law (V=IR) and the power equation (P=VI).
Enter any two values to solve for the other two.
Formula & relationships
P = V × I (Power Law)
P = I² × R (derived from both)
P = V² / R (derived from both)
Given any two variables, the other two can be determined from these four relationships.
1Worked example: a 12V supply across a 4Ω resistor. V=12, R=4 → I = 12/4 = 3 A, P = 12 × 3 = 36 W
Common questions
What is Ohm's Law?
Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R. It is the foundational relationship in electrical circuit analysis.
Why are there four variables if Ohm's Law only has three (V, I, R)?
Ohm's Law (V=IR) relates voltage, current and resistance. The power equation (P=VI) adds a fourth variable. Together, they form a system where knowing any two values determines the other two — which is what this calculator does.
Does Ohm's Law apply to all components?
Ohm's Law applies to ohmic (linear) resistors. Non-linear components like diodes, transistors and LEDs do not obey Ohm's Law across their full operating range — their resistance changes with voltage/current.