Ohm's Law Calculator

About Ohm's Law

Ohm's Law is the fundamental relationship between voltage (V), current (I) and resistance (R) in an electrical circuit. Formulated by Georg Simon Ohm in 1827, it states that the voltage across a conductor is directly proportional to the current flowing through it, provided temperature remains constant.

The core equation is V = I × R, which can be rearranged to solve for any of the three quantities. Combined with the power equation P = V × I, you can derive all four values from any two known quantities.

The Four Ohm's Law Formulas

• V = I × R — Voltage equals current multiplied by resistance.
• I = V ÷ R — Current equals voltage divided by resistance.
• R = V ÷ I — Resistance equals voltage divided by current.
• P = V × I = I² × R = V² ÷ R — Power in watts, derived from any two quantities.

How to Use This Calculator

1. Click the pair of quantities you already know (e.g. V + I).
2. Enter the values in the input fields, selecting the correct units.
3. The remaining two quantities are calculated instantly and displayed below, along with the formula used.

Results are displayed in auto-selected units — for example, a very small current will be shown in milliamps (mA) rather than amps (A) for readability.

Practical Applications

Ohm's Law is used daily by electronics engineers and hobbyists to size resistors, calculate safe current limits, determine power dissipation in components, and design circuits for microcontrollers, LEDs, motors and power supplies. Understanding it is essential for any work with Arduino, Raspberry Pi, or discrete circuit design.