Voltage Divider Calculator

A load connected at the output node sits electrically in parallel with R2, and two resistors in parallel always have less combined resistance than either alone — so the effective 'R2' the formula sees is smaller than the R2 you set, pulling Vout down. The lower the load's resistance relative to R2, the bigger the drop.

The ratio R2/(R1+R2) sets Vout regardless of the absolute values, so pick the absolute values based on the current you can tolerate: smaller resistors draw more current through the divider (wasting power) but resist being pulled down by a load better; larger resistors waste less power but are more easily disturbed. A few kilohms to a few hundred kilohms is the typical range for a lightly loaded divider.

Only if it draws a small, constant, known current — otherwise no. Its output sags under load in a way that depends on exactly how much current is drawn, which is rarely acceptable. A linear or switching regulator is the right tool for actually supplying power at a lower voltage.

There isn't one in general — the ratio depends entirely on what Vout you need relative to Vin, since Vout/Vin equals R2/(R1+R2). Pick the ratio first from the voltages, then choose the absolute resistor sizes based on how much current the divider can afford to waste.