Ohm's Law Calculator
Solve for voltage, current or resistance and get the power — pick what to find.
Results update as you type.
About this calculator
Ohm's law relates voltage, current and resistance with V = I × R. Choose which quantity to solve for, enter the other two, and this calculator returns the missing value plus the electrical power P = V × I. It works for any DC resistive circuit and the resistive part of an AC one.
Frequently asked questions
What is Ohm's law?
Ohm’s law states that the current through a conductor is proportional to the voltage across it: V = I × R. Rearranged, I = V / R and R = V / I.
How do I find electrical power from Ohm’s law?
Power is voltage times current, P = V × I. Using Ohm’s law you can also write it as P = I² × R or P = V² / R — all three give the same watts.
Which two values do I enter?
Pick the quantity you are missing in "Solve for", then enter the other two. To find resistance, enter voltage and current; the resistance box is ignored.
Results are estimates for general guidance only, not financial, medical or tax advice.