Ohm's Law Calculator
Enter any two of voltage, current, resistance, or power and this Ohm's law calculator instantly finds the other two — runs 100% in your browser with no upload.
V = 12 V I = 2 A R = 6 Ω P = 24 W
🔒 Calculated in your browser — nothing is uploaded.
What this Ohm's law calculator does
Enter any two of the four electrical quantities — voltage V in volts, current I in amps, resistance R in ohms, and power P in watts — and the calculator instantly derives the remaining two. Leave the fields you want to find blank, type the two you know, and the results update live as you type. It works for every valid pair, whether you know voltage and current, resistance and power, or any other combination.
The formulas it uses
The tool combines Ohm's law with the electrical power relationships. Ohm's law states V = I × R, so resistance is R = V ÷ I and current is I = V ÷ R. Power ties them together through P = V × I, which also gives P = I² × R and P = V² ÷ R. From any two known values the calculator picks the matching pair of equations and solves the rest. When you supply resistance and power it takes a square root, since V = √(P × R) and I = √(P ÷ R). If a combination would require dividing by zero or taking the root of a negative number, it tells you instead of returning a nonsense answer.
Frequently asked questions
How many values do I need to enter?
Exactly two. Ohm's law links voltage, current, resistance, and power, so any two of them fully determine the other two. Enter fewer than two and there is nothing to solve; enter more than two and the inputs could conflict, so the tool asks you to clear the extras.
Is anything I type uploaded to a server?
No. Every calculation runs locally in your browser with JavaScript. The values you enter are never sent, stored, or logged anywhere.
Why do I sometimes get an error instead of an answer?
Some combinations have no valid solution — for example a current of zero when solving for resistance would divide by zero, and a negative resistance or power under a square root has no real result. The calculator flags these instead of showing a wrong number.