Voltage Divider Calculator

What is a Voltage Divider?

A voltage divider is a passive linear circuit that produces an output voltage that is a fraction of its input voltage. It consists of two resistors (R1 and R2) connected in series between the input voltage (Vin) and ground. The output voltage (Vout) is taken from the junction between the two resistors.

Voltage dividers are used extensively in electronics to set bias points, create reference voltages, attenuate signals, and interface between components operating at different voltage levels — for example, connecting a 5V microcontroller output to a 3.3V input.

The Voltage Divider Formula

The output voltage is calculated using the formula:

Vout = Vin × R2 ÷ (R1 + R2)

R1 is the top resistor (connected to Vin) and R2 is the bottom resistor (connected to ground). The ratio R2 / (R1 + R2) determines what fraction of Vin appears at the output. If R1 equals R2, Vout is exactly half of Vin.

Important Limitations

This calculation assumes the output is unloaded (no current drawn from Vout). When a load is connected, the effective resistance changes and Vout will drop. For loaded dividers, choose resistor values significantly lower than the load impedance to minimise this effect.

Voltage dividers are not efficient for power delivery — they waste energy as heat in the resistors. For power regulation, use a dedicated voltage regulator or switching converter instead.