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Solve voltage, current, resistance and power.
Ohm's Law describes the relationship between voltage, current and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance.
Enter any two of the three quantities and the calculator solves for the remaining one and the power dissipated. It is the core tool for sizing resistors, checking circuit currents and verifying supply voltages.
From any two known values the other two follow: with V and I, R = V ÷ I; with V and R, I = V ÷ R; with I and R, V = I × R.
Ohm's Law links three quantities through one equation, so knowing any two fixes the third. Entering three would over-constrain the problem, and entering one leaves it unsolvable.
That is normal for high resistances on low voltages — for example 12 V across 100 kΩ gives only 0.12 mA. The calculator shows extra decimals so small currents remain readable.
For purely resistive AC loads, use RMS values of voltage and current and the same equations hold. Reactive loads (capacitors, inductors, motors) need impedance and power-factor corrections that this calculator does not model.
Power is the rate of energy use, P = V × I. Substituting V = I × R gives P = I² × R, and I = V ÷ R gives P = V² ÷ R, so power can be found from any two of the three quantities.