Ohm's Law Calculator
Enter any two known electrical values to calculate the missing value using V = I × R.
A QUICK WALKTHROUGH
How to use this tool
- Choose the value you want to calculate.
- Enter the two known values with their units.
- Calculate the result and review the power relationship shown below.
The three forms of Ohm's law
Voltage equals current multiplied by resistance (V = I × R). Rearranging gives current = voltage ÷ resistance and resistance = voltage ÷ current.
Power is included
When the three electrical values are known, the calculator also shows power in watts using P = V × I. Power is an ideal DC calculation and does not model AC phase, efficiency, or component heating.
Private browser calculation
Values are validated and calculated locally in your browser. Nothing is uploaded or stored by this page.
GOOD TO KNOW
Common questions
What is Ohm's law?
Ohm's law describes the relationship between voltage, current, and resistance: V = I × R.
Which two values should I enter?
Enter any two of voltage, current, and resistance. The calculator derives the third.
Can resistance or current be zero?
Resistance must be greater than zero when calculating current or power. Current must be nonzero when calculating resistance.
Does this calculator support AC circuits?
It provides the basic ideal relationship for scalar values. It does not calculate impedance, phase angle, RMS values, or AC power factor.