Voltage Divider Calculator
Enter the input voltage and the two resistor values to find the output voltage across R2 and the current through the divider.
Vout = Vin × R2 / (R1 + R2)
How a voltage divider works
A voltage divider is two resistors in series across a voltage source, with the output taken from the junction between them. The output voltage is Vout = Vin × R2 / (R1 + R2) — R2's share of the total resistance determines its share of the input voltage.
The current flowing through the divider is the same through both resistors (since they're in series): I = Vin / (R1 + R2). This calculator shows that current in milliamps, since voltage dividers are typically used with relatively high resistances and small currents.
Frequently asked questions
What is a voltage divider used for?
Voltage dividers are commonly used to scale down a voltage for a sensor or microcontroller input, or to create a reference voltage from a higher supply voltage.
Why is the output voltage proportional to R2?
Since the same current flows through both resistors (they're in series), the voltage drop across each resistor is proportional to its resistance — so the fraction of the total voltage that appears across R2 is simply R2's share of the total resistance.
Does a voltage divider work well under heavy load?
No — if a significant current is drawn from the output node, it changes the effective resistance and the output voltage drops from the calculated value. Voltage dividers work best when the output feeds a high-impedance load, like an op-amp or ADC input.