Electronics Tools

Voltage Divider Calculator

Calculate output voltage, input voltage, or resistor values instantly.

This bidirectional tool solves for any parameter in a voltage divider circuit (Vin, R1, R2, or Vout). It supports unit selection (Ω, kΩ, MΩ) for simpler input and accurate results.

Pro Feature: It calculates the Power Dissipation (to prevent burning components) and suggests the Nearest Standard Resistor (E24) for practical, real-world builds.

Circuit Parameters

Enter Any 3
V
V

Calculation Status

Waiting for input…

Live Circuit Analysis

Visual
Vin — V R1 — Ω Vout — V R2 — Ω

Component Analysis

Resistor 1
Power: —
Std (E24): —
Resistor 2
Power: —
Std (E24): —

Common Questions

What is a Voltage Divider?
A voltage divider is a simple circuit that turns a large voltage into a smaller one. Using just two series resistors (R1 and R2) connected to an input voltage (Vin), you can create an output voltage (Vout) that is a fraction of the input.
Does load resistance affect Vout?
Yes! This calculator assumes an “unloaded” output (connected to a high-impedance input like an Arduino pin). If you connect a load with low resistance (like a motor or LED), it acts in parallel with R2, lowering Vout.
Why calculate Resistor Power?
Even small resistors can burn up if the current is too high. Most standard resistors are rated for 0.25 Watts (1/4W). This tool calculates the power dissipated by R1 and R2 so you can choose components that won’t overheat.

Key Equations

Voltage Output

Vout = Vin × ( R2 / (R1 + R2) )

Input Voltage

Vin = Vout × ( (R1 + R2) / R2 )

Find R1

R1 = R2 × ( (Vin / Vout) − 1 )

Find R2

R2 = R1 / ( (Vin / Vout) − 1 )

How to Use This Calculator

Design a voltage divider in 3 simple steps.

1

Enter 3 Values

Fill in any three known parameters. For example, to find the Output Voltage, enter Vin, R1, and R2.

2

Set Units

Use the dropdown menu to select Ω, kΩ, or MΩ for resistors. This saves you from typing extra zeros.

3

Check Power & Standard Values

Review the Component Analysis box. Ensure the Power Dissipation is less than your resistor’s rating (usually 0.25W) and note the nearest E24 standard value for purchasing.