Ohm's Law Calculator
Enter any two values — voltage, current, or resistance — to calculate the third.
Enter any 2 of the 3 values. Leave the one you want to calculate blank.
Ohm's Law formulas
V = I × R (Voltage = Current × Resistance)
I = V / R (Current = Voltage / Resistance)
R = V / I (Resistance = Voltage / Current)
P = V × I (Power = Voltage × Current)
How to use Ohm's Law
Ohm's Law states that the voltage across a resistor equals the current through it multiplied by its resistance (V = I × R). Enter any two known values and the calculator solves for the third. Power (P = V × I) is shown as a bonus result — it's the energy consumed or delivered per second, measured in watts.
For resistor color code decoding, use the Resistor Color Code Calculator.
Private & free — this tool runs entirely in your browser.