Voltage Divider×
There are different voltage dividers. This app handles resisitive dividers, when the impedances, R1 and R2, are purely resistive. See Wikipedia's Voltage Divider article for other voltage dividers.

Enter three of the four values. When entering a third value, the last value will be calculated for you.

Vin  
R1 Ω
 Vout  
R2 Ω