Voltage Divider Calculator

Work out the output of a resistor divider, or the R2 for the voltage you need – for example 5 V to 3.3 V for an ESP32 input.

  • Free
  • Solve for R2
  • E12 values
  • Divider current
Output voltage–
Current through divider–
R2 for wanted output–
Standard resistor–

How to calculate a voltage divider

  1. 1

    Enter input and resistors

    Type the input voltage, R1 (top) and R2 (bottom).

  2. 2

    Read the output

    The output voltage and the current through both resistors update instantly.

  3. 3

    Find R2 for a target

    Enter the voltage you want; the calculator gives the exact R2 and the next standard value.

Why use this voltage divider calculator?

  • Both directions

    Calculates the output from two resistors, or the second resistor for the output you need.

  • Instant and private

    Results update as you type; nothing is sent anywhere.

  • Free, no sign-up

    No account, no ads in the way, works on phone and desktop.

  • Formulas shown

    The page explains how each result is calculated, so you can check it.

Popular uses

  • Measuring batteries with an ADC
  • 5 V to 3.3 V logic levels
  • Sensor inputs on Arduino and ESP32
  • Setting regulator outputs
  • Bias voltages
  • Electronics homework

Frequently asked questions

What is the voltage divider formula?

Vout = Vin × R2 / (R1 + R2). With 12 V, R1 = 10 kΩ and R2 = 4.7 kΩ the output is 3.84 V.

How do I choose R2 for a wanted voltage?

R2 = Vout × R1 / (Vin − Vout). For 3.3 V from 5 V with R1 = 10 kΩ, R2 ≈ 19.4 kΩ; the next E12 value is 22 kΩ.

Can a voltage divider power a circuit?

No. A divider is for signals and measurements; once a load draws current, the output drops. Use a regulator to supply power.