Skip to main content
FreeToolkit .ai

Voltage Divider Calculator Calculate output voltage or required resistor value for voltage divider circuits.

Voltage Divider Calculator illustration
🔢

Voltage Divider Calculator

Calculate output voltage or required resistor value for voltage divider circuits.

1

Choose Mode

Calculate output voltage from resistors, or find R2 for a target voltage.

2

Enter Values

Input Vin, R1, and R2 (or desired Vout).

3

View Results

See output voltage, divider ratio, current flow, and power dissipation.

Loading tool...

What Is Voltage Divider Calculator?

The Voltage Divider Calculator computes the output voltage of a two-resistor voltage divider circuit, or finds the required R2 resistor value to achieve a desired output voltage. A voltage divider is one of the most fundamental circuits in electronics, used to reduce voltage, create reference voltages, and interface between components with different voltage levels. The calculator shows the divider ratio, current flow through the resistors, and power dissipation in each resistor — important for selecting appropriate component ratings.

Why Use Voltage Divider Calculator?

  • Two modes: calculate Vout or find required R2
  • Shows current flow and power dissipation per resistor
  • Displays divider ratio for quick reference
  • Essential for circuit design and voltage level conversion

Common Use Cases

Level Shifting

Convert 5V logic signals to 3.3V for microcontroller interfacing.

Sensor Reading

Scale sensor output voltage to match ADC input range.

Reference Voltage

Create stable reference voltages from a supply rail.

Battery Monitoring

Scale battery voltage down for measurement by a microcontroller.

Technical Guide

The voltage divider equation: Vout = Vin × R2 / (R1 + R2). Rearranged to find R2: R2 = R1 × Vout / (Vin − Vout). Current through the divider: I = Vin / (R1 + R2). Power dissipation: P_R1 = I² × R1, P_R2 = I² × R2. The divider ratio = R2 / (R1 + R2). Important considerations: the voltage divider equation assumes no load (or negligible load current). When a load is connected, it appears in parallel with R2, changing the effective R2 and reducing the output voltage. For loaded dividers, use R values much smaller than the load impedance (rule of thumb: 10× or more).

Tips & Best Practices

  • 1
    Use resistor values much smaller than the load impedance to minimize loading effects
  • 2
    Higher resistance values reduce power consumption but increase noise sensitivity
  • 3
    Match resistor tolerances for precision applications
  • 4
    Consider temperature coefficients for precision voltage references

Related Tools

Ohm's Law Calculator - free online tool

Ohm's Law Calculator

Calculate voltage, current, resistance, or power using Ohm's Law and the power equation.

🔢 Math & Calculators
Resistor Color Code Calculator - free online tool

Resistor Color Code Calculator

Decode resistor values from color bands with visual selector for 4-band and 5-band resistors.

🔢 Math & Calculators
Percentage Calculator - free online tool

Percentage Calculator

Calculate percentages, percentage change, and what percent one number is of another.

🔢 Math & Calculators
BMR Calculator - free online tool

BMR Calculator

Calculate your Basal Metabolic Rate using Mifflin-St Jeor and Harris-Benedict equations.

🔢 Math & Calculators

Frequently Asked Questions

Q What is a voltage divider?
A voltage divider is a simple circuit with two resistors in series. The output voltage is taken from the junction between the resistors and is a fraction of the input voltage.
Q Can a voltage divider increase voltage?
No, a passive voltage divider can only reduce voltage. To increase voltage, you need an active circuit (boost converter, transformer, etc.).
Q What happens when I connect a load?
Connecting a load places it in parallel with R2, which lowers the effective resistance and reduces the output voltage. To minimize this effect, choose resistor values much lower than the load impedance.
Q Can I use a voltage divider for power applications?
Voltage dividers waste energy as heat and have poor load regulation. Use voltage regulators or DC-DC converters for power applications.
Q How do I choose R1 and R2 values?
First, determine the ratio needed (Vout/Vin). Then choose values that give acceptable current draw — typically 1-10 mA for signal applications.

About This Tool

Voltage Divider Calculator is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.