Voltage Divider Calculator
Find the output voltage and current of a two-resistor voltage divider from Vin, R1, and R2.
How it works
A voltage divider is just two resistors in series across a supply. Tap the junction between them and you get a fraction of the input voltage — a cheap way to scale a signal down to a level your circuit can handle.
The formula is Vout = Vin × R2 ÷ (R1 + R2). With 9 volts in, R1 at 1 kΩ and R2 at 2 kΩ, you get 9 × 2000 ÷ 3000 = 6 volts out. Swap the resistor sizes and the ratio flips.
The same current runs through both resistors, and the tool shows it too. That current matters: too little and noise creeps in, too much and you waste power, so dividers are a balancing act between stiffness and efficiency.
Frequently asked questions
Can I connect a load to the output?
You can, but a load in parallel with R2 changes the ratio and lowers Vout. Dividers work best feeding a high-impedance input like an ADC pin or an op-amp, where the load draws almost no current.
How do I pick resistor values?
Choose the ratio first for the voltage you want, then scale both resistors up or down together. Bigger resistors waste less power; smaller ones resist loading effects better.
Why does the current matter?
The current sets how much power the divider burns and how stiff the output is. A stiffer divider (lower resistance) holds its voltage better under load but wastes more energy as heat.