Ohm's law
Calculate voltage, current, or resistance.
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Tool guide
Ohm's law: how it works
Practical information to understand the result and use this tool correctly.
About Ohm's law
Ohm's law relates the three basic electrical quantities of a resistive circuit: V = I × R, with voltage in volts (V), current in amperes (A), and resistance in ohms (Ω).
Enter any two of the three values and the tool solves the third: I = V / R, R = V / I, and V = I × R. Power follows as P = V × I in watts.
The calculation runs locally in the browser and assumes an ohmic conductor: resistance stays constant with temperature, and AC reactance is out of scope.
How to use it
- 1Enter two of the three values: voltage (V), current (A), or resistance (Ω).
- 2The missing value and the power in watts update instantly.
- 3Copy the result. Nothing is uploaded to any server.
Frequently asked questions
- What is the formula of Ohm's law?
- V = I × R: voltage in volts equals current in amperes times resistance in ohms. Rearranged, I = V / R and R = V / I.
- How do I calculate power from Ohm's law?
- P = V × I in watts. Combining with Ohm's law also gives P = I² × R and P = V² / R.
- Does it work for AC circuits?
- Only for purely resistive loads. AC circuits with coils or capacitors need impedance, not just resistance.