Voltage Divider Calculator
Enter the input voltage and the two resistors. Add a load to see how it pulls the output down.
Leave the load empty for an unloaded divider. A load in parallel with R2 lowers the output.
Worked examples
Equal resistors
12 V with 10 kilohm and 10 kilohm
6 V
Half the input voltage.
With a load
12 V, 10 kilohm, 10 kilohm and a 10 kilohm load
4 V
The lower leg becomes 5 kilohm.
About Voltage Divider Calculator
A voltage divider is two resistors in series across a supply, with the output taken from the point where they join. It is the simplest way to turn a higher voltage into a lower one, and it appears everywhere from sensor inputs to reference levels and test points. This calculator gives the output voltage from the input voltage and the two resistor values.
A divider rarely works alone. Whatever you connect to the output sits in parallel with the lower resistor and pulls the voltage down. Enter the load resistance to see the real output, as well as the unloaded figure, the current taken from the supply and the power turned to heat in each resistor, so you can check that small parts are not overloaded.
How to use Voltage Divider Calculator
- Enter the input voltage.
- Type R1, the resistor from the input to the output, and R2, the resistor from the output to ground.
- If something is connected to the output, enter its resistance as the load.
- Read the output voltage, the unloaded output, the current and the power in each resistor.
Common uses
- Scaling a 12 volt signal down for a 3.3 volt input
- Setting a bias or reference voltage
- Checking how much a meter or sensor loads a divider
- Teaching potential dividers in physics lessons
Frequently asked questions
What is the voltage divider formula?
The output voltage is the input voltage multiplied by R2 and divided by the sum of R1 and R2. R2 is the resistor between the output and ground.
How does a load change the output?
A load in parallel with R2 lowers the effective lower resistance, so the output drops. Ten kilohm resistors giving 6 volts from 12 volts fall to 4 volts if a 10 kilohm load is added.
How can I keep the output steady under load?
Make the divider resistors much smaller than the load, ideally ten times smaller. The price is more current wasted in the divider, so a buffer or a regulator is better for anything that needs real current.
Can I use a divider to power something?
Only for loads that draw a tiny current. For anything that draws real current, use a regulator, because the output of a divider changes with the load and wastes power.