How to Calculate Voltage with Ohm's Law

Calculates voltage with Ohm's law V = current × resistance. Current is in amperes, resistance in ohms, and voltage in volts.

Explanation

Given the current through a component and its resistance, Ohm's law gives the voltage across it.

V = I R

$V$ is the voltage, in volts (V)
$I$ is the current, in amperes (A)
$R$ is the resistance, in ohms (Ω)

For a fixed resistance, doubling the voltage doubles the current. For a fixed current, a resistor twice as large needs twice the voltage across it.

Example

The defaults are a current of 2 A and a resistance of 50 Ω.

V = 2 \times 50 = 100\,\mathrm{V}

The voltage is 100 V.

Notes

Ohm's law holds for ohmic conductors: wires and ordinary resistors, where current stays proportional to voltage. Diodes and lamp filaments, whose resistance shifts with direction or with temperature, do not obey it directly.

Resistance drifts with temperature, and metals resist more when hot, so the formula applies at a steady temperature.

Keep the units consistent. Divide milliamps by 1000 to get amps, and multiply kilohms by 1000 to get ohms. Conveniently, milliamps times kilohms comes out directly in volts.