Ohm's Law Calculator

Ohm's law calculator solves for voltage, current, resistance, and power in a DC circuit when you supply any two of voltage, current, and resistance. It applies V = I × R together with P = V × I, so a single pair of inputs reveals all four electrical quantities. This is a staple tool for electronics hobbyists, students, and technicians sizing resistors or checking circuit behaviour.

Formula

V = I × R and P = V × I

V

Voltage across the component in volts (V)

I

Current through the component in amperes (A)

R

Resistance in ohms (Ω)

P

Power dissipated in watts (W)

How it works

1. Enter exactly two of the three quantities: voltage (V), current (A), or resistance (Ω).
2. The calculator derives the missing quantity from Ohm's law (V = IR), then computes power as P = V × I.
3. All four values — voltage, current, resistance, and power — are returned so you can read the complete circuit picture.

Worked example

Frequently asked questions

How many values do I need to enter?

Exactly two of voltage, current, and resistance. With two known quantities the calculator solves for the third using Ohm's law and then calculates the power. Entering fewer or more than two returns an error.

How is power calculated here?

Power is computed as P = V × I once voltage and current are known. This is equivalent to the alternative forms P = I²R and P = V²/R, all of which give the same result for a resistive load.

Why can resistance or current not be zero?

Dividing by zero is undefined, so the calculator rejects a zero current when solving for resistance and a zero resistance when solving for current. A true short circuit (R = 0) implies infinite current, which has no finite answer.

Does Ohm's law apply to AC circuits?

This calculator covers DC and purely resistive loads. In AC circuits with capacitance or inductance you must use impedance instead of plain resistance and account for phase, which this simple form does not model.

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