Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's Law. Enter any two values to find the other two.
How it works
Ohm's Law states that V = I × R, where V is voltage in volts, I is current in amps, and R is resistance in ohms. Power is calculated as P = V × I. Enter any two of the three values (voltage, current, resistance) and leave the third as 0 — the calculator will solve for all four quantities including power.
Example
A 120V circuit powers a load with 12Ω resistance. Current = 120 / 12 = 10A. Power = 120 × 10 = 1,200W (1.2 kW). On your electric bill, running this load for 1 hour costs roughly $0.15 at the US average rate of $0.13/kWh.
Frequently asked questions
Who discovered Ohm's Law?
Georg Simon Ohm, a German physicist, published his findings in 1827. He discovered the linear relationship between voltage and current through a conductor at constant temperature, which became the foundational law of electrical circuits.
Does Ohm's Law apply to AC circuits?
Ohm's Law applies directly to resistive AC loads. For circuits with inductors or capacitors, the concept extends to impedance (Z) measured in ohms, replacing resistance in the formula. The relationship becomes V = I × Z.
What is the power formula in electricity?
P = V × I (power equals voltage times current). It can also be expressed as P = I² × R (when you know current and resistance) or P = V² / R (when you know voltage and resistance). Power is measured in watts (W).
What happens if resistance increases in a circuit?
If voltage stays constant and resistance increases, current decreases proportionally (I = V/R). This is why adding loads in series increases total resistance and reduces current, while adding loads in parallel decreases total resistance and increases current.
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