Voltage Divider Calculator
Output Voltage6.0000 V
Current0.006000 A
The Voltage Divider Calculator finds the output voltage tapped between two series resistors driven by a source voltage, the classic R1–R2 divider used to scale signals and set reference levels. It also reports the current flowing through the series chain. Enter the input voltage and both resistor values to see how the divider splits the supply in proportion to R2 over the total resistance.
Formula
Vout = Vin × R2 / (R1 + R2); I = Vin / (R1 + R2)
- Vin
- Source (input) voltage in volts
- R1
- Top series resistor in ohms
- R2
- Bottom resistor in ohms; output is taken across it
- Vout
- Output voltage across R2 in volts
How it works
- Enter the input (source) voltage Vin, the top resistor R1, and the bottom resistor R2 (the output is measured across R2).
- Output voltage is Vin × R2 / (R1 + R2): the supply is divided in the ratio of R2 to the total resistance.
- Series current is Vin / (R1 + R2). Both results are rounded to four decimal places, and the calculator rejects negative resistances or a zero total resistance.
Worked example
A 12 V supply with R1 = 1 kΩ and R2 = 2 kΩ.
- Total resistance = 1000 + 2000 = 3000 Ω.
- Vout = 12 × 2000 ÷ 3000 = 8 V.
- Current = 12 ÷ 3000 = 0.004 A (4 mA).
Output voltage 8 V with 0.004 A (4 mA) flowing through the divider.
Frequently asked questions
- What is a voltage divider used for?
- It scales a higher voltage down to a lower one using two resistors, commonly to create a reference voltage, bias a transistor, or bring a signal into the range an ADC or microcontroller pin can read.
- Does the formula account for a load on the output?
- No. The calculation assumes an ideal, unloaded output. Connecting a load across R2 effectively parallels it with R2, lowering the output voltage, so use a load with much higher resistance than R2.
- How is the current through the divider found?
- With no external load, the same current flows through both resistors in series, equal to the input voltage divided by the total resistance, R1 plus R2.
- Why can’t the total resistance be zero?
- Dividing by zero is undefined and would represent a dead short across the supply. The calculator requires both resistances to be non-negative and their sum to be greater than zero.