Ohm's Law Calculator
Compute voltage, current, resistance and power from any two values.
Enter any two of voltage (V), current (I), resistance (R) or power (P) — the calculator solves for the other two using Ohm's law and the power formulas.
Common use cases
- Size a resistor for an LED based on supply voltage and target current
- Compute power dissipation in a resistor for thermal margin
- Verify a multimeter reading against expected values
- Solve electrical homework problems quickly
Frequently asked questions
What are the formulas?▾
V = IR · P = VI · P = I²R · P = V²/R. Any two values uniquely determine the others.
What if I enter 3 values?▾
We use the first two valid inputs we find. For consistency, leave two blank to be explicit about which to solve for.
Does it work for AC?▾
These formulas are for DC circuits. AC requires impedance, phase and RMS — beyond the scope of basic Ohm's law.