Voltage Divider Calculator
Calculate output voltage, resistor values, or input voltage
Result
Common Applications
5V → 2.5V (50%)
Two equal resistors, halves the voltage
5V → 2.86V (ADC ref)
Common for scaling analog signals
12V → 3.84V
12V battery to 3.3V logic level
9V → 2.23V
9V battery sensing for Arduino
Voltage Divider Formula
Vout = Vin × (R2 / (R1 + R2))
A voltage divider uses two resistors in series to reduce voltage. The output voltage (taken between the resistors) is a fraction of the input voltage, determined by the resistor ratio.
Important Considerations
Loading effect: If you connect a load to Vout, it acts as a parallel resistance with R2, changing the output voltage. For accurate voltage division, the load impedance should be at least 10× greater than R2.
Power dissipation: Current flows through both resistors continuously. Choose resistor values high enough to minimize wasted power, but low enough to be stable against noise. 10kΩ is a common starting point.
Current calculation: I = Vin / (R1 + R2). With 5V and 20kΩ total, that's 0.25mA.