Ohm's Law Calculator

Ohm's law states that voltage equals current times resistance (V = I x R). Combined with the power law P = V x I, it links voltage, current, resistance and power into one connected set of equations.

Exactly two. From any two of voltage, current, resistance and power the other two are fully determined, which is why the tool offers six pairings to choose from.

Volts for voltage, amperes for current, ohms for resistance and watts for power. If your current is in milliamps, divide by 1000 first, so 20 mA becomes 0.02 A.

The four working relations are V = I x R, P = V x I, P = I^2 x R and P = V^2 / R. The calculator selects the right combination for whichever pair you supply.

Dividing voltage by zero resistance implies infinite current, which is not physically meaningful, so the Voltage plus Resistance case rejects a resistance of zero.

Yes. Voltage plus Power finds current and resistance, and Current plus Power finds voltage and resistance. In those modes the shared quantity cannot be zero, since dividing power by zero volts or zero amps is undefined.

It returns voltage as the square root of power times resistance, and current as the square root of power divided by resistance. Both resistance and power must be non-negative for the roots to be real.

The tool applies the direct current form of Ohm's law with plain resistance. For AC you would use impedance and account for phase, so treat these results as valid for resistive loads or as an approximation.

Yes. All four values are computed in your browser, so nothing you enter about your circuit is sent to a server.