Engineering

Voltage Divider Calculator — Free 2026

Calculate the output voltage and current of a resistive voltage divider circuit instantly.

Input Voltage (V) Please enter a valid number.

R1 — Top Resistor (Ohms) Please enter a valid number.

R2 — Bottom Resistor (Ohms) Please enter a valid number.

Results

—

Output Voltage (V)

—

Current (mA)

—

Divider Ratio

—

Total Power (mW)

How It Works

Enter input voltage
Enter resistor values
Read the results

Understanding Voltage Dividers

A voltage divider is one of the most common and useful circuits in electronics. It consists of two resistors connected in series between a voltage source and ground. The output voltage, taken at the junction between the two resistors, is a predictable fraction of the input voltage determined by the resistor ratio. The formula Vout = Vin × R2 / (R1 + R2) lets you calculate the exact output for any combination of resistors and input voltage.

How Voltage Dividers Work

When current flows through two series resistors, the voltage drops across each resistor in proportion to its resistance. If both resistors are equal, the voltage splits evenly — giving you half the input voltage. By choosing different resistor values, you can produce any output voltage from nearly zero up to (but never exceeding) the input voltage. This makes voltage dividers ideal for level shifting, sensor interfacing, and creating reference voltages. For a deeper understanding of the underlying principles, try our Ohm's law calculator.

Loading Effect and Limitations

The voltage divider formula assumes no load is connected to the output, meaning the output draws zero current. In practice, any connected load acts as a parallel resistor with R2, reducing the effective resistance and lowering the output voltage. To minimize loading, choose resistor values much smaller than the load impedance, or use a buffer amplifier (such as an op-amp voltage follower) between the divider output and the load. Voltage dividers are also not suitable for high-power applications since they waste energy as heat in the resistors.

Common Applications

Voltage dividers appear in countless circuits: biasing transistors, reading potentiometers, scaling analog sensor signals for ADC inputs, creating reference voltages for comparators, and converting 5V logic signals to 3.3V levels. Many microcontroller projects use voltage dividers to safely read battery voltage or interface with sensors that output voltages outside the controller's input range. For related calculations, check out the unit converter for converting between electrical units.

Frequently Asked Questions

What is a voltage divider?

A voltage divider is a simple circuit with two resistors in series that produces an output voltage that is a fraction of the input voltage. The output voltage is taken across one of the resistors, and the ratio depends on the resistor values: Vout = Vin × R2 / (R1 + R2).

What is the voltage divider formula?

The voltage divider formula is Vout = Vin × R2 / (R1 + R2), where Vin is the input voltage, R1 is the top resistor connected to Vin, and R2 is the bottom resistor connected to ground. The output voltage is measured across R2.

When should I use a voltage divider?

Voltage dividers are commonly used for reading sensors, creating reference voltages, level shifting between logic families, biasing transistors, and interfacing 5V sensors with 3.3V microcontrollers. They work best with high-impedance loads that draw minimal current.

Why is my voltage divider output different from expected?

The most common reason is loading effect — when the load connected to the output has an impedance comparable to R2, it acts as a parallel resistor and reduces the effective R2 value, lowering the output voltage. Use a buffer amplifier or choose lower resistor values to minimize this effect.