FREE ELECTRICIAN TOOLS
Ohm’s Law Calculator
Use this calculator to quickly calculate Voltage, Current, Resistance, or Power based on the data you have. Enter in any two to calculate the others.
Note: Change units by using the dropdown selectors on the right. Click “Clear All” to start a new calculation.
How to Calculate with Ohm’s Law Manually
Ohm’s Law and Joule’s Law are two fundamental principles that form the foundation of most electrical calculations. They describe the relationship between the four basic electrical quantities: Voltage (V), Current (I), Resistance (R), and Power (P).
In simple terms, these laws work together so that if you know any two of these values, you can always calculate the other two. This is essential for electricians when sizing components, diagnosing faults, or designing circuits.
Here is Ohm’s Law rearrangeed to calculate each of Voltage, Resistance, and Current:
If you want to calculate Power, you’ll need to incorporate Joule’s Law: