Voltage Divider Calculator

Calculate output voltage, resistor values, or input voltage for a resistive voltage divider circuit.

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1. Choose what you want to solve for - output voltage, a resistor value, or input voltage. 2. Enter the input voltage (Vin) in volts for your power source. 3. Enter the values for R1 (upper resistor) and R2 (lower resistor) in ohms, kilohms, or megohms. 4. Optionally enter a load resistance to see the real-world output voltage under load conditions. 5. Review the output voltage, divider current, and power dissipated by each resistor. 6. Adjust resistor values until the output matches your target voltage within tolerance.

About This Tool

A voltage divider is one of the most common circuits in electronics. It uses two resistors in series to produce an output voltage that is a fraction of the input voltage. This simple arrangement is used everywhere - from sensor signal conditioning and reference voltage generation to biasing transistors and reading potentiometers.

This calculator solves the voltage divider equation in any direction. Enter the input voltage and both resistor values to find the output voltage, or specify the desired output voltage and one resistor to find the other. It also shows the current flowing through the divider and the power dissipated by each resistor, helping you verify that your components are operating within safe limits.

For more advanced use, the tool accounts for load resistance. An unloaded voltage divider behaves ideally, but connecting a load to the output draws additional current and lowers the output voltage. By entering the load resistance, you can see the actual output voltage under real-world conditions.

Formula / How It Works

Vout = Vin x R2 / (R1 + R2) | With load: Vout = Vin x (R2 || RL) / (R1 + (R2 || RL))

Frequently Asked Questions

A voltage divider is a simple circuit with two resistors (R1 and R2) connected in series between a voltage source and ground. The output voltage is taken from the junction between the two resistors. The output voltage equals the input voltage multiplied by R2 / (R1 + R2).
When a load is connected to the output, it acts as a resistor in parallel with R2, reducing the effective lower resistance. This lowers the output voltage below the ideal calculated value. For minimal loading effects, the load resistance should be at least 10 times greater than R2.
Voltage dividers are generally not suitable for powering devices because they have poor voltage regulation - the output voltage drops when current is drawn by the load. For powering devices, use a voltage regulator (linear or switching) instead. Voltage dividers are best for signal-level applications.
First, use the voltage divider formula to find the required ratio R2 / (R1 + R2). Then choose standard resistor values that match this ratio. Keep total resistance low enough for your application but high enough to minimize wasted current. Typical values range from 1k to 100k ohms depending on the circuit.
The basic voltage divider formula is Vout = Vin x R2 / (R1 + R2), where Vin is the input voltage, R1 is the upper resistor (connected to Vin), and R2 is the lower resistor (connected to ground). With a load resistance RL, the formula becomes Vout = Vin x (R2 parallel RL) / (R1 + R2 parallel RL).

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