⚡Ohm's Law Calculator
Enter any two of voltage, current, resistance, or power — the rest are solved instantly with a formula triangle and steps shown.
Free Ohm's Law Calculator
Need to solve a circuit problem fast? Our free Ohm's Law Calculator finds voltage, current, resistance, or power the moment you enter any two related values. Type in what you know, and get the answer instantly — complete with a visual formula triangle so you can see exactly how the values relate.
Unit conversions are built in, so you can mix volts and millivolts, amps and milliamps, or ohms and kilohms without doing the math yourself. Every result comes with the formula used and the substitution shown step by step, making it easy to check your circuit homework or verify a real-world measurement.
Whether you're a student learning basic electronics or an engineer double-checking a quick calculation, this tool gives you accurate answers with the working shown. No sign-up, no downloads, no limits. See the About page or the FAQ for more.
About the Ohm's Law Calculator
Features
Solve for V, I, R, or P
Automatically picks the correct formula from any valid pair of known values.
Formula triangles
Visual V/I/R and P/V/I triangles highlight which quantity is being solved.
Unit conversion
Mix volts/millivolts, amps/milliamps, and ohms/kilohms/megaohms freely.
Step-by-step working
Every result shows the formula and substitution with your actual entered values.
Frequently Asked Questions
How does the Ohm's Law calculator work?
Enter the two values you know among voltage, current, resistance, and power, and it calculates the rest instantly.
Is it free?
Completely free, no sign-up, downloads, or limits.
What is Ohm's Law?
Ohm's Law states V = IR: voltage equals current times resistance.
Can it calculate power too?
Yes, using P=VI, P=I²R, or P=V²/R depending on which values you provide.
Does it handle different units?
Yes, each field has a unit dropdown (mV, kV, mA, kΩ, etc.) with automatic conversion.
Does it show the formula used?
Yes, along with a visual formula triangle and the substitution of your actual values.
What if I enter a negative resistance?
The calculator flags negative or zero resistance as physically invalid rather than returning a nonsensical answer.
Can I use this to check circuit homework?
Yes, it's designed for quickly verifying voltage, current, resistance, or power calculations.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive with the formula triangle scaling to fit the screen.