Ohm's Law

Calculate voltage, current, resistance and electrical power with a step-by-step explanation.

Before you calculate

Understanding Ohm's Law

Voltage (V) is an electrical potential difference, current (I) is the flow of charge and resistance (R) limits that flow. Enter any two to find the third and the power consumed by a resistive load.

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Step 1

Input parameters

Enter or change any two quantities. The third updates automatically. You can also edit the calculated field—it then becomes an input.

Voltage (V, V)Input

Enter a positive value.

Current (I, A)Calculated

Automatically calculated · Edit to use as an input.

Resistance (R, Ω)Input

Enter a positive value.

Step 2

Calculated results

Voltage (V) · given12 V

Current (A) · calculated2 A

Resistance (Ω) · given6 Ω

Power (W) · calculated24 W

For a linear resistive load, voltage and current are in phase. These are DC values or RMS values for purely resistive AC circuits. Reactance and nonlinear loads are excluded.

1. Calculate current

Divide the voltage across the resistance by its resistance.

I=\frac{V}{R}

I=\frac{12}{6}\approx 2\,\mathrm{A}

2. Calculate electrical power

Voltage multiplied by current gives electrical power.

P=V\times I

P=12\,\times\,2\approx 24\,\mathrm{W}

3. Verify power using resistance

The same result follows from the resistive power relationship.

P=I^2\times R

P=(2)^2\,\times\,6\approx 24\,\mathrm{W}

The calculation uses full precision internally; only the displayed numerical steps are rounded.