Use this free Ohm’s Law calculator to find voltage, current, resistance or power. Enter any two values and click Calculate — the tool computes the rest using V = I × R and P = V × I.
Ohm’s Law Calculator
Enter any two values, leave the unknown blank, then click Calculate.
Ohm’s Law Formula
Ohm’s law relates voltage (V), current (I) and resistance (R):
V = I × R • I = V / R • R = V / I • P = V × I
How to Use This Calculator
- Enter any two of the three quantities (V, I, R).
- Leave the value you want to find blank.
- Click Calculate to get the missing value plus the power.
Worked Example
If a 12 V battery drives a current of 2 A, the resistance is R = V / I = 12 / 2 = 6 Ω, and the power dissipated is P = V × I = 12 × 2 = 24 W.
Frequently Asked Questions
What is Ohm’s law?
Ohm’s law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R.
How do you calculate current and resistance?
To find current use I = V / R; to find resistance use R = V / I. Power is P = V × I.
What is the unit of resistance?
The SI unit of resistance is the ohm (Ω).