The voltage divider is one of the most fundamental and commonly used circuits in electronics. Whether you are scaling down a 5V signal to be read by a 3.3V microcontroller, or interfacing an analog sensor like a thermistor or photoresistor with an ADC, you will find yourself calculating voltage dividers constantly.

The Core Formula

A voltage divider consists of two resistors ($R_1$ and $R_2$) connected in series across an input voltage ($V_{in}$). The output voltage ($V_{out}$) is taken from the connection between the two resistors. The calculation relies on Ohm's Law and Kirchhoff's Voltage Law, resulting in the following formula:

To speed up your prototyping, I've created the interactive calculator below. Simply input your source voltage and resistor values (with automatic scaling for Ohms, Kilo-ohms, and Mega-ohms) to instantly find your output voltage.