Voltage Divider Calculator
Output voltage, current and power for a two-resistor divider.
How it works
Vout = Vin x R2 / (R1 + R2), as long as nothing is drawing current from the output.
That caveat is the whole difficulty. Any load sits in parallel with R2 and pulls the output down. The rule of thumb is that the load should be at least ten times R2 for the unloaded formula to hold; below that, enter it above and read the real figure.
Low resistor values give a stiff, load-tolerant output and waste current continuously. High values save power and are easily disturbed. Dividers are for signals and references, never for powering anything.
Common questions
Why is my output lower than the formula says?
Something is loading it. Even a multimeter's 10 MΩ input matters against megohm resistors. Enter the load resistance above to see the real output.
Can I use a divider to drop supply voltage for a circuit?
No. The output voltage collapses as soon as the load draws current, and the resistors waste power as heat regardless. Use a regulator.