Ohm's Law Calculator
Calculate voltage, current, resistance and power using Ohm's law.
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Ohm's law is the foundation of electrical engineering - it describes the relationship between voltage, current and resistance in a circuit. Enter any two values and this calculator finds the third plus the power dissipated. It works for DC circuits and AC circuits at unity power factor.
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Frequently asked questions
Divide voltage by current. A 12V circuit drawing 2A has a resistance of 6 Ω. This is Ohm's law: R = V/I.
Power equals voltage times current: P = V × I. A 12V supply delivering 2A produces 24 watts of power.
Divide voltage by resistance. A 120V circuit with 60 Ω resistance draws 2A of current. Use I = V/R.
Ohm's law works for AC circuits when you replace resistance with impedance. For purely resistive AC loads, the formula is identical. Reactive loads require complex impedance calculations.
Power in watts equals voltage squared divided by resistance: P = V²/R. A 240V heater with 20 Ω resistance dissipates 2880 watts.