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Voltage Divider Calculator

Calculate Vout, divider current, and resistor power dissipation instantly with unit conversion and sourcing shortcuts.

Enter Vin, R1, and R2 to calculate Vout, divider current, and resistor power with automatic unit conversion.

Schematic guide

Standard voltage divider topology

SVG

Set values

Adjust the source voltage and resistor pair directly below the topology.

Live sync

Input voltageSet the available source voltage before the divider network.

Top resistor R1R1 sits between Vin and Vout.

Bottom resistor R2R2 sits between Vout and ground.

Quick design read

Balanced

Target output is 8 V with 400 uA through the divider.

This output is better suited to general voltage monitoring or front-end sensing rather than direct low-voltage MCU pins.

Vin

12 V

R1 / R2

10 kOhm / 20 kOhm

Live results

Zero delay

Vout

8 V

From 12 V, the divider scales to 8 V.

Divider current

400 uA

Output ratio

66.67% of Vin

R1 power

1.6 mW

R2 power

3.2 mW

Conversion Hook

Need components for your project? Search parts & check stock instantly.

After calculating the target output, move straight into sourcing with resistor-series suggestions, quick search, and RFQ shortcuts.

Suggested sourcing query

Yageo 10k 20k 1% 0603 resistor

BOM Upload

Upload BOM for a Quick Quote

Turn this single resistor calculation into a full-project sourcing request with one click.

Yageo RC Series

General-purpose thick film chips that fit 10k / 20k resistor pair designs for cost-sensitive boards.

0603 / 0805

UniOhm WR Series

Stable resistance tolerance options for control boards, industrial sensing, and common divider networks.

0603 / 1206

Fenghua Precision Resistors

Useful for quick-turn BOM fulfillment when mainstream resistor values need an alternative supply path.

0402 / 0603

Upload BOM / Get a Quick Quote Open RFQ form

SEO Content

What is a Voltage Divider?

A voltage divider calculator helps engineers quickly estimate the output voltage of a resistor divider circuit before choosing real components. A voltage divider is a simple resistor network that scales an input voltage down to a predictable output voltage, and it is widely used in ADC front ends, reference biasing, comparator thresholds, and signal conditioning.

This resistor divider formula page covers the voltage divider schematic, how to calculate Vout, how to choose R1 and R2, and what practical design issues can cause the measured output to drift away from the ideal formula.

Voltage Divider Formula and Design Notes

Core formula

V_{out} = V_{in} \cdot \frac{R_{2}}{R_{1} + R_{2}}

V_{out} = V_{in} \\cdot \\frac{R_2}{R_1 + R_2}

Choose resistor values high enough to limit current, but not so high that leakage and ADC sampling distort the result.
Check resistor power dissipation, especially when dividing from 24 V, 48 V, or higher industrial rails.
If the divider drives an ADC input, validate source impedance against the ADC sample-and-hold requirements.

How to Choose R1 and R2 for a Voltage Divider

Start by choosing the target output voltage and the acceptable divider current. Lower resistance values waste more current but are less sensitive to leakage and input loading. Higher resistance values improve power efficiency but can become unstable when driving an ADC input or a noisy analog node.

For ADC inputs

Keep the effective source impedance low enough for the ADC sample-and-hold capacitor. Many MCU designs stay in the low-kOhm to tens-of-kOhm range unless a buffer is added.

For low-power rails

Increase resistance to reduce current draw, but verify leakage, resistor tolerance, and board contamination do not push Vout outside the allowed sensing window.

Common Mistakes in Voltage Divider Design

Ignoring the input load

The basic resistor divider formula assumes no load. If the next stage pulls current, the effective R2 changes and Vout drops.

Choosing resistors that are too large

Very high resistance values reduce current consumption, but leakage current, ADC sampling current, and contamination on the PCB can create noticeable error.

Skipping power and voltage rating checks

Even when the formula is correct, resistor package limits and voltage stress can still make the design unreliable on higher rails.

Reference Table

Divider ratio quick table

Target	R1 : R2	Typical use
1/2 Vin	1 : 1	Midpoint bias, comparator thresholds
1/3 Vin	2 : 1	MCU sensing from higher rails
1/4 Vin	3 : 1	24 V to 6 V monitoring front end
1/5 Vin	4 : 1	Wide-input industrial measurement

Tap a row to load a matching example into the calculator.

Application Examples

Common divider targets

Source rail	Target Vout	Example ratio
24 V	5 V	38k : 10k
24 V	3.3 V	62k : 10k
12 V	5 V	14k : 10k
5 V	3.3 V	5.1k : 10k

Tap a row to autofill Vin, R1, and R2 at the top.

Design Snapshot

Vin

12 V

R1 / R2

10 kOhm / 20 kOhm

Search-ready pair

10k / 20k resistor pair

FAQ Schema

Frequently asked questions about resistor dividers

What is the best resistor range for a voltage divider?

Many low-power divider designs start in the 1 kOhm to 100 kOhm range, then adjust upward or downward based on ADC input impedance, noise sensitivity, and allowable current draw.

Can I use a standard resistor divider for high-voltage applications?

Only after checking resistor voltage rating, creepage, power dissipation, and safety requirements. High-voltage dividers often need series stacks and dedicated high-voltage parts.

Why does my measured Vout differ from the calculated result?

Real-world Vout can shift because of resistor tolerance, input loading, ADC sampling current, leakage paths, and source voltage variation.

How do I choose resistor tolerance for a divider network?

Use the tightest tolerance your error budget needs. For sensing and reference scaling, 1% is common, while precision measurement may need 0.1% or matched resistor networks.