Voltage Divider Calculator

The voltage divider is one of the most fundamental and widely used circuits in electronics. Two resistors in series, connected between a supply voltage and ground, produce an output voltage at their junction proportional to the resistance ratio: Vout = Vin × R2 / (R1 + R2). Simple, elegant, and requiring no active components, voltage dividers appear in virtually every electronic circuit as biasing networks, reference voltage generators, signal attenuators, and level shifters.

The voltage divider principle follows directly from Kirchhoff's Voltage Law and Ohm's Law. With the same current flowing through both series resistors (I = Vin / (R1 + R2)), the voltage drop across R2 equals I × R2 = Vin × R2/(R1+R2). The ratio R2/(R1+R2) is the divider ratio — ranging from 0 (when R2 = 0) to 1 (when R1 = 0). Any intermediate voltage between 0 and Vin is achievable by selecting the appropriate ratio.

The unloaded voltage divider is ideal — it produces exactly Vout = Vin × R2/(R1+R2) when no current is drawn from the output node. However, connecting a load resistance RL across R2 changes the effective bottom resistance to R2||RL = (R2 × RL)/(R2 + RL), reducing Vout below the unloaded value. This 'loading effect' is a critical practical consideration: for the divider to maintain accurate output voltage, the load resistance should be much larger than R2 (typically RL ≥ 10 × R2 for less than 10% error).

Choosing divider resistor values involves balancing two competing requirements: lower resistance values minimize loading error but increase quiescent current and power dissipation; higher resistance values reduce power waste but increase susceptibility to loading by the downstream circuit. A practical rule of thumb: set divider current to 10× the maximum load current expected, keeping loading error below 10%. For precision reference dividers, use 0.1% tolerance resistors and keep divider current high relative to load current.

Voltage dividers are used for: ADC input voltage scaling (5 V signal to 3.3 V MCU input); battery voltage monitoring (scaling high voltage to ADC range); transistor base biasing (establishing operating point); DAC output attenuation; audio pot (potentiometer) volume controls; and in Wheatstone bridge sensor circuits where four resistors form two voltage dividers that are compared for differential measurement.

This calculator provides both unloaded and loaded output voltages, along with divider current, power dissipation in R1, and loading error percentage — giving a complete picture of voltage divider performance under practical operating conditions.