Voltage Divider Calculator
Calculate the output voltage of a two-resistor voltage divider.
Output Voltage (Vout)
Current (I)
Total Power (P)
The Voltage Divider Formula
A voltage divider is a simple circuit of two resistors in series. The input voltage Vin is applied across both resistors, and the output is taken across the lower resistor R2. The same current flows through both resistors, so the output voltage is a fixed fraction of the input.
- Vout = Vin · R2 / (R1 + R2) - Output voltage
- I = Vin / (R1 + R2) - Current through the divider
- P = Vin² / (R1 + R2) - Total power dissipated
Loading Effect and Output Impedance
The simple formula assumes nothing draws current from the output. In reality, connecting a load resistor in parallel with R2 reduces the effective resistance and pulls Vout lower — this is the loading effect. The output impedance of the divider equals R1 in parallel with R2. To keep loading errors small, the load impedance should be much larger than this output impedance (a common rule of thumb is at least ten times larger).
Common Uses
- Scaling a signal down to a level a microcontroller ADC can read.
- Reading resistive sensors such as thermistors and photoresistors.
- Setting a stable reference voltage or a bias point in analog circuits.
- Level-shifting and basic potentiometer (variable divider) controls.