Question 1

What is Ohm's law?

Accepted Answer

Ohm's law states that the current through a resistor is proportional to the voltage across it: V = I × R. Combined with the power law P = V × I, you can derive any of voltage, current, resistance and power from any two of them.

Question 2

Which two values do I need to enter?

Accepted Answer

Any two of V, I, R and P. The calculator supports all six combinations and computes the remaining two automatically. If you enter zero, one, or more than two values, it asks you to enter exactly two.

Question 3

How is power calculated?

Accepted Answer

Power is P = V × I. Using Ohm's law this also equals P = I² × R and P = V² / R, so the calculator can find power from any valid pair of inputs.

Question 4

How do I find resistance or voltage from power?

Accepted Answer

From power and voltage, R = V² / P and I = P / V. From power and current, V = P / I and R = P / I². From power and resistance, V = √(P × R) and I = √(P / R).

Question 5

Does this work for AC circuits?

Accepted Answer

This calculator uses the ideal DC model with a linear resistor. For AC you must account for reactance, impedance and power factor, and real components also drift with temperature and are not perfectly linear, so treat the result as a first-order estimate.

Ohm’s LawCalculator

Ohm’s Law
Calculator