Overview
Ohm’s law links voltage, current, and resistance in many circuits. If you know two quantities, you can solve for the third—when the resistor behaves linearly.
Know two, find the third
If a resistor is ohmic, V, I, and R are linked by V = IR.
Watch units
Volts, amperes, and ohms must be consistent—convert milliamps before dividing.
Ideal model
Real components can heat up and deviate; treat the calculator as the ideal relationship.
Try the calculator
Use the free Ohm's Law Calculator for live numbers, then come back to this guide anytime you need a quick refresher.