# Voltage Divider Calculator

> Calculate voltage divider step by step: Vout = Vin × R2 ÷ (R1 + R2).

Page: https://freecalculator.tech/tools/voltage-divider-calculator
Last reviewed: 2026-11-03

## Formula

Vout = Vin × R2 ÷ (R1 + R2). With a load RL, R2 is replaced by R2 ∥ RL = R2·RL ÷ (R2 + RL).

- The unloaded formula assumes nothing draws current from the output.
- Adding a load lowers Vout; the calculator shows this when you enter a load.
- R1 + R2 must be above zero.
- Vout = Vin × R2 ÷ (R1 + R2). With a load RL, R2 is replaced by R2 ∥ RL = R2·RL ÷ (R2 + RL).
- Inputs used: Input voltage, R1 (top resistor), R2 (bottom resistor), Load resistance on output (optional).

## Inputs

- Input voltage
- R1 (top resistor)
- R2 (bottom resistor)
- Load resistance on output (optional)

## Worked example: 12 V into 10 kΩ and 4.7 kΩ

Unloaded divider output.
1. Vout = 12 × 4,700 ÷ 14,700.
2. Vout = 3.837 V.

## Common questions

### Can I power a device from a voltage divider?

Usually not. Any load current changes the output voltage and wastes power in the resistors. Use a regulator for supplies; dividers suit sensing and reference inputs.

### How do I pick resistor sizes?

Use values low enough that the load draws much less current than the divider (a common rule is ten times less), but high enough to keep wasted current small.

### Why does the load field matter?

A meter, ADC input or device in parallel with R2 lowers the effective bottom resistance. Entering it shows the real output voltage.

### How do I use the Voltage Divider Calculator?

Enter the required values for Input voltage, R1 (top resistor), R2 (bottom resistor), Load resistance on output (optional). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Voltage Divider Calculator use?

Vout = Vin × R2 ÷ (R1 + R2). With a load RL, R2 is replaced by R2 ∥ RL = R2·RL ÷ (R2 + RL). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Voltage Divider Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Ignores resistor tolerance (±1% or ±5% shifts the output).
- DC or resistive only.
- Does not model source resistance.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this voltage divider calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-2

## Cite this page

- APA: Free Calculator. (2026, November 3). Voltage Divider Calculator. https://freecalculator.tech/tools/voltage-divider-calculator
- MLA: "Voltage Divider Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/voltage-divider-calculator.
- Link: Voltage Divider Calculator — Free Calculator, https://freecalculator.tech/tools/voltage-divider-calculator