Voltage Divider Calculator
Vout from Vin and two resistors, plus the current and wasted power.
The divider formula
Vout = Vin × R2 / (R1 + R2)
The two resistors split the input voltage in proportion to their values. 12 V across 10 kΩ and 4.7 kΩ puts 3.84 V across the 4.7 k.
The classic mistake: loading the divider
The formula assumes nothing is connected to Vout. Any load in parallel with R2 lowers the output; the rule of thumb is the load should be at least 10× R2. Dividers are for reference voltages and sensing (reading a battery with an ADC), never for powering anything: the standing current burns power all day even when the output is unused.