Voltage Divider Calculator

How It Works

A voltage divider consists of two resistors (R1 and R2) connected in series between a voltage source and ground. The output voltage is taken from the node between the resistors:

Vout = Vin × R2 / (R1 + R2)

The current through the divider is: I = Vin / (R1 + R2)

When to Use a Voltage Divider

• Sensor reading: Scale a 0-5V sensor output to 0-3.3V for a microcontroller
• Voltage measurement: Measure high voltages with a low-voltage ADC
• Transistor biasing: Set the operating point for BJT amplifiers
• Reference voltage: Create a stable reference for comparators
• Level shifting: Interface between circuits running at different voltages

Load Impedance Warning

The output voltage formula assumes no load (or infinite load resistance). When a load is connected, it appears in parallel with R2, effectively lowering the combined resistance and dropping the output voltage.

Rule of thumb: Load resistance should be at least 10× the value of R2 for the output to remain within 10% of the calculated value.

Practical Design Tips

• Use 1% tolerance resistors for precision applications
• Keep total resistance between 1k and 100k ohms
• Add a buffer (op-amp voltage follower) if driving any significant load
• Consider temperature effects on resistor values for precision work

Note: This calculator assumes ideal resistors with no load connected to the output.