Ohm's Law Calculator
Enter any two of voltage, current, resistance and power to calculate the other two with Ohm's law and the power formulas.
How to use
- 1Fill in any two values and leave the other two blank.
- 2Results use volts, amps, ohms and watts.
How it's calculated
V = I × R; P = V × I = I²R = V² ÷ R.
Frequently asked questions
What is Ohm's law?
The current through a conductor is proportional to the voltage across it: V = IR.
Does it apply to AC?
For resistive loads, yes (using RMS values). With capacitors and inductors you need impedance instead of resistance.
How do I size a resistor's power rating?
Calculate P = I²R and choose a resistor rated at least double that for a safety margin.