Ohm's Law Calculator
Voltage, Current, Resistance & Power
Enter any two values and leave the other two blank — we'll calculate the rest.
Ready for Calculation
Enter exactly two known values above to solve for the rest.
Understanding Ohm's Law
Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit: V = I × R. Combined with the power formula P = V × I, any two known values are enough to solve for the other two.
The Water Analogy
Voltage is like water pressure, current is like flow rate, and resistance is like the narrowness of a pipe. More pressure or a wider pipe means more flow.
Adding Power
Power (in watts) tells you the rate of energy conversion — combined with V = IR, it lets you solve for any of the four quantities from just two knowns.
The Ohm's Law Formulas
V = I × R | I = V ÷ R | R = V ÷ I
P = V × I | P = I² × R | P = V² ÷ R
Which Two to Enter?
Any pair works: Voltage & Current, Voltage & Resistance, Current & Resistance, or either paired with Power.
Key Takeaways
- Exactly Two Inputs: Enter exactly two of the four values — entering more or fewer will produce inconsistent or missing results.
- DC Circuits: These formulas apply directly to simple DC circuits; AC circuits with reactive components require more advanced impedance calculations.
- Foundational Formula: Ohm's Law underlies nearly every basic electronics calculation, from LED resistor sizing to power supply design.