Formula
The unloaded output is the input times the lower resistor's share of the total:
Vout = Vin × R2 / (R1 + R2)
R1 is the upper resistor and R2 is the lower one. Current is the input divided by both resistors. Ohm's law for a single resistor stays on its own page.
Assumptions
- Nothing else draws current from the output.
- Both resistors stay at the values you type.
- The input is a steady voltage.
Worked example
9 volts across 1,000 ohms and 2,000 ohms puts 6 V across the lower resistor.
Input definitions
- Input voltage
- Volts applied across both resistors. Zero is allowed.
- Upper resistor
- Ohms between the input and the output node.
- Lower resistor
- Ohms between the output node and ground.
Limitations
A load across the lower resistor changes the output. This page does not include that load, resistor tolerance, or a safe power rating.
Questions
Which resistor is R2?
The lower resistor, the one connected to ground. The output is measured across it.
What if I connect a load?
The load sits in parallel with the lower resistor, so the output falls. Enter the combined resistance as the lower resistor if you already know it.