Ohm's Law Calculator

Ohm's law is V = I × R: the voltage across a resistor equals the current through it times its resistance. The law applies to ideal resistors in DC circuits and to RMS values in AC circuits with purely resistive loads.

Start with P = V × I (the basic definition of electrical power) and substitute Ohm's law. Replace V with I × R to get P = I² × R. Replace I with V / R to get P = V² / R. All three forms describe the same power dissipation.

Because two independent values determine the other two through Ohm's law and the power relationships. Entering three creates an overdetermined system; if the third does not match what Ohm's law predicts, there is no consistent answer. Clear extra fields before computing.

An ohm is the SI unit of electrical resistance: 1 ohm is the resistance that produces 1 ampere of current when 1 volt is applied. Symbol is the Greek letter omega (Ω). Larger units include kΩ (1,000 Ω) and MΩ (1 million Ω).

For purely resistive AC loads, yes; substitute RMS voltage and RMS current. For circuits with capacitance or inductance, the relationships use complex impedance instead of pure resistance, and power has real (W), reactive (VAR), and apparent (VA) components. This calculator handles the basic resistive case only.

No. The calculator is a math tool for the basic electrical relationships. Real electrical work involves code compliance, conductor sizing, overcurrent protection, grounding, and safety procedures that this tool does not address. Consult a licensed electrician for permitted electrical work.