Find the output voltage of a two-resistor voltage divider — free and instant.
A voltage divider uses two resistors in series to produce a smaller output voltage from a larger input: Vout = Vin × R2 ⁄ (R1 + R2), where Vout is measured across R2. This is one of the most common building blocks in analog electronics, used for level-shifting sensor signals, setting a reference voltage, and countless similar tasks.
The output only depends on the *ratio* of R1 to R2, not their absolute values — doubling both resistors keeps Vout exactly the same, which is why voltage dividers are described by that ratio as much as by specific resistor values.
For the ideal voltage calculation, only the ratio of R1 to R2 matters — 1kΩ/2kΩ gives the same Vout as 10kΩ/20kΩ. In real circuits, the absolute values matter too, since they affect how much current is drawn and how sensitive the divider is to whatever it’s connected to.
It’s a convention based on how the circuit is drawn — R1 is the resistor closer to the input, R2 closer to ground, and the divided voltage is taken from the junction between them, which sits across R2.
Vout becomes exactly half of Vin, since R2/(R1+R2) = R2/2R2 = 0.5 when the two resistors match.