Engineering calculator

Voltage Divider Calculator, Output Voltage & Power Dissipation

Calculate output voltage and power dissipation for resistive voltage divider circuits. Enter Vin and two resistor values to find Vout.

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V
Ω

Top resistor (connected to Vin)

Ω

Bottom resistor (connected to ground)

Output Voltage (Vout)

–

Vout = Vin × R2 / (R1 + R2)

Current

–

Through the divider

Power in R1

–

Heat dissipated

Power in R2

–

Heat dissipated

Total Power

–

Total dissipation

Voltage Ratio

–

Vout / Vin

How CalcMesh solves a voltage divider

A two-resistor voltage divider outputs Vout = Vin × R2 / (R1 + R2). We compute the output voltage, and the resistor value needed to hit a target, directly from this exact formula.

The result assumes negligible load current draw at the output; where a load matters we explain the correction in our methodology.

According to the U.S. National Institute of Standards and Technology, resistor tolerances of 1% to 5% are typical, so we remind you that a real divider’s output can drift several percent from the ideal figure.

Voltage Divider Guide

How It Works

A voltage divider consists of two resistors (R1 and R2) connected in series between a voltage source and ground. The output voltage is taken from the node between the resistors:

Vout = Vin × R2 / (R1 + R2)

The current through the divider is: I = Vin / (R1 + R2)

When to Use a Voltage Divider

  • Sensor reading: Scale a 0-5V sensor output to 0-3.3V for a microcontroller
  • Voltage measurement: Measure high voltages with a low-voltage ADC
  • Transistor biasing: Set the operating point for BJT amplifiers
  • Reference voltage: Create a stable reference for comparators
  • Level shifting: Interface between circuits running at different voltages

Load Impedance Warning

The output voltage formula assumes no load (or infinite load resistance). When a load is connected, it appears in parallel with R2, effectively lowering the combined resistance and dropping the output voltage.

Rule of thumb: Load resistance should be at least 10× the value of R2 for the output to remain within 10% of the calculated value.

Practical Design Tips

  • Use 1% tolerance resistors for precision applications
  • Keep total resistance between 1k and 100k ohms
  • Add a buffer (op-amp voltage follower) if driving any significant load
  • Consider temperature effects on resistor values for precision work

Note: This calculator assumes ideal resistors with no load connected to the output.

Worked example, 12 V → 3.3 V sense rail

Labelled unloaded divider (not a power-supply design):

  • Vin = 12 V, R1 = 10 kΩ, R2 = 3.9 kΩ.
  • Vout = Vin×R2/(R1+R2) = 12×3.9/13.9 ≈ 3.37 V (near a 3.3 V ADC top).
  • Divider current I = Vin/(R1+R2) ≈ 0.86 mA; P_R1≈7.5 mW, P_R2≈2.9 mW.
  • If a 10 kΩ load sits on Vout, R2∥10k ≈ 2.8 kΩ and Vout falls, keep R_load ≫ R2.

After you run the numbers

What to do with the results

  • Vout = Vin×R2/(R1+R2) is the open-circuit ideal; any load parallels R2 and pulls Vout down.
  • Rule of thumb: R_load ≥ 10×R2 keeps the drop near the calculated value.
  • Pick resistor wattage from the shown P_R1/P_R2, not from Vin alone.
  • Do not use a divider as a bulk PSU, regulators/DC-DC belong there; dividers are for sensing/bias.

Methodology & Assumptions

This circuit tool rearranges textbook electrical identities (Ohm, power, divider) on the values you enter. Component tolerances are not modelled—treat outputs as design starts.

How this circuit node runs

Ohm/power/divider tools rearrange textbook electrical identities. Real components carry tolerances the page does not invent. Published domain formulas govern the identities; when an agency updates rates or thresholds we refresh defaults and the page lastmod.

Frequently Asked Questions

What is a voltage divider?
A voltage divider is a simple circuit that uses two resistors in series to produce an output voltage that is a fraction of the input voltage. The output is taken from the junction between the two resistors. It is one of the most common circuits in electronics, used for level shifting, sensor reading, biasing transistors, and creating reference voltages.
Why does a load affect the output voltage?
When you connect a load to the output of a voltage divider, the load resistance appears in parallel with R2, effectively reducing the combined resistance and lowering the output voltage. For the voltage divider formula to be accurate, the load resistance should be at least 10 times greater than R2. This is why voltage dividers are best suited for low-current, high-impedance applications.
Can I use a voltage divider as a power supply?
Generally no. Voltage dividers are not efficient power supplies because they waste power as heat in the resistors and their output voltage drops significantly under load. For powering circuits, use a voltage regulator (like the LM7805 for 5V) or a DC-DC converter instead. Voltage dividers are best for signal conditioning, sensing, and biasing.
How do I choose resistor values for a voltage divider?
Start by deciding your desired output voltage and choosing a ratio. For example, to halve a voltage, use equal resistors. Keep total resistance high enough to minimize wasted current (typically 1k-100k ohms total), but low enough relative to your load impedance. Standard practice is to use the lowest values that keep quiescent current under 10% of the load current.

This page identifies the inputs, method, and limitations behind its estimates. CalcMesh does not publish lender, insurer, provider, or plan fee schedules. Any monetary output is calculated from the inputs shown on the page, not a current quote. Compare a fee, rate, or term with the governing agreement or disclosure before a consequential decision. Calculator outputs are not professional advice. Circuit identities here rearrange the volts, amps, and resistances you enter—no lab certificate is implied. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.

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Inputs, defaults, and authoritative sources
Input Default Source / authority
All inputs Domain-typical defaults Editorial methodology, CalcMesh 2026