What Is a Voltage Divider?

A voltage divider is a simple circuit that uses two resistors in series to reduce a higher voltage to a lower one. It is one of the most fundamental circuits in electronics, used in sensor interfaces, signal conditioning, reference voltage generation, and level shifting.

Core Formula: The output voltage (Vout) is determined by the ratio of the two resistors (R1 and R2) and the input voltage (Vin), following the formula: Vout = Vin × R2 / (R1 + R2)

This calculator helps you quickly compute output voltages, find the right resistor values for your target voltage, and understand how load resistance affects your circuit's performance.

When to Use a Voltage Divider

Level Shifting

Convert a 5V signal to 3.3V for a microcontroller input

Sensor Reading

Scale down a 12V sensor output to a safe ADC range

Reference Voltage

Create a stable reference from a power supply

Audio Attenuation

Reduce signal levels between audio stages

Battery Monitoring

Measure battery voltage with a low-voltage ADC

How to Use the Calculator

Calculate Output Voltage

Select Mode

Choose the Calculate Vout tab in the calculator interface

Enter Input Voltage

Input the Input Voltage (Vin) and select the appropriate unit (mV, V, or kV)

Set Resistor Values

Enter R1 and R2 values with your preferred units (Ω, kΩ, or MΩ)

View Results

The calculator instantly displays output voltage, current, power dissipation, and voltage ratio

Find Required Resistor Value

Select Mode

Choose the Find Resistor tab in the calculator

Define Voltages

Enter both Input Voltage (Vin) and Desired Output Voltage (Vout)

Specify Known Resistor

Select which resistor you already have (R1 or R2) and enter its value

Get Recommendations

View the required resistor value plus the nearest E24 standard value with actual output voltage and error percentage

Analyze Load Effects

Enable Load Analysis

Toggle Load Resistance (RL) on in the calculator

Enter Load Value

Input the load resistance value that will be connected to the output

Compare Results

Compare the loaded Vout with the ideal (no-load) Vout to see the impact

Check Warnings

A warning appears if the load causes more than 5% deviation from the ideal voltage

Additional Features

Precision Control

Adjust decimal places from 2 to 6 for your required accuracy level

Quick Examples

Load common circuit presets with one click to see practical applications

Circuit Diagram

View a live schematic that updates with your actual values in real-time

Formula Reference

Quick access to all voltage divider formulas and calculation methods

Key Features

Two Calculation Modes

Switch between Calculate Vout (forward calculation from known resistors) and Find Resistor (reverse calculation to find the resistor needed for a target voltage). Both modes provide real-time results as you type.

Calculate Vout

Forward Calculation

Known: Vin, R1, R2
Calculate: Vout
Use case: Testing existing circuits
Shows: Current, power, ratio

Find Resistor

Reverse Calculation

Known: Vin, Vout, one resistor
Calculate: Missing resistor
Use case: Designing new circuits
Shows: E24 standard suggestions

E24 Standard Resistor Suggestions

When finding a resistor value, the calculator automatically suggests the nearest E24 series standard value. It shows the actual output voltage you would get with the standard resistor and the percentage error compared to your desired voltage, helping you select components from real-world inventory.

Practical advantage: E24 suggestions ensure you can actually build your circuit with commonly available resistors, eliminating the frustration of designing with theoretical values that don't exist in standard component catalogs.

Load Resistance Analysis

Real circuits have loads connected to the voltage divider output. Enable the Load Resistance option to see how a parallel load affects your output voltage. The calculator warns you when the load causes significant deviation (more than 5%), and suggests using lower divider resistor values for better accuracy.

Important consideration: A voltage divider without load analysis can lead to unexpected behavior in real circuits. Always account for the load resistance to ensure your design performs as expected when connected to actual components.

Interactive Circuit Diagram

A live SVG circuit diagram updates with your actual values, showing Vin, R1, R2, Vout, and current flow. When load resistance is enabled, the load resistor appears as a dashed element connected in parallel with R2.

SI Prefix Support

Select appropriate units for each value: millivolts to kilovolts for voltage, ohms to megaohms for resistance. Results automatically scale to the most readable unit — for example, 0.001 A displays as 1 mA.

Complete Circuit Analysis

Beyond output voltage, the calculator shows the voltage division ratio, total circuit current, and power dissipated in each resistor — essential information for selecting appropriately rated components.

Voltage Ratio

Understand the proportional relationship between input and output

Circuit Current

Know the total current draw for power budget planning

Power Dissipation

Select resistors with adequate power ratings for reliability

Frequently Asked Questions

What is the voltage divider formula?

The basic voltage divider formula is Vout = Vin × R2 / (R1 + R2), where Vin is the input voltage, R1 is the top resistor (connected to Vin), and R2 is the bottom resistor (connected to ground). The output voltage is taken at the junction between R1 and R2.

Key insight: The output voltage is always a fraction of the input voltage, determined by the ratio of R2 to the total resistance (R1 + R2).

Why does my actual output voltage differ from the calculated value?

The basic formula assumes no current is drawn from the output (no load). In practice, any connected circuit draws current, which effectively reduces R2 by placing a parallel resistance. Use the Load Resistance feature to see the actual output voltage with your load connected.

Common mistake: Designing a voltage divider without considering the load resistance is one of the most frequent errors in electronics. Always account for the load to avoid unexpected voltage drops.

What are E24 standard resistor values?

E24 is a series of 24 preferred resistor values per decade (1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1), available in multiples of 10. Most resistors sold commercially follow these standard values with 5% tolerance.

Example: If you need a 4.5kΩ resistor, the nearest E24 values are 4.3kΩ and 4.7kΩ. The calculator helps you choose which one gives you the closest output voltage to your target.

How do I choose appropriate resistor values?

The ratio R2/(R1+R2) determines the output voltage, so many resistor pairs can produce the same Vout. Consider these guidelines:

Lower values (1kΩ–10kΩ) provide better load regulation but consume more power
Higher values (100kΩ–1MΩ) save power but are more sensitive to load effects
Common range: 1kΩ to 100kΩ for most applications

Resistor Range	Power Consumption	Load Sensitivity	Best For
1kΩ – 10kΩ	High	Low	High-current loads, audio circuits
10kΩ – 100kΩ	Medium	Medium	General purpose, sensor interfaces
100kΩ – 1MΩ	Low	High	Battery-powered, high-impedance inputs

Can a voltage divider increase voltage?

No. A resistor voltage divider can only reduce voltage. The output voltage is always less than or equal to the input voltage. To increase voltage, you need an active circuit such as a boost converter or charge pump.

Physical limitation: Passive resistor networks cannot add energy to a circuit. Voltage step-up requires active components like inductors, capacitors, and switching elements.

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