Voltage divider calculator for R1, R2 and Vout

A free browser-based voltage divider calculator that computes Vout from R1/R2 or finds optimal resistor values for a target voltage. Includes load resistance effects, E24 standard value matching, tolerance analysis, output impedance, and power dissipation for each resistor.

How to Use the Voltage Divider Calculator

Choose mode and enter values

Select "Solve for Vout" if you know R1 and R2, or "Solve for R1/R2" if you need a specific output voltage.

Add load resistance (optional)

Enter the load resistance if one is connected to the output. This affects the actual Vout due to current drawn by the load.

Read the results

See Vout, divider current, power dissipation, output impedance, and tolerance range. Use E24 suggestions for real components.

Design resistive voltage dividers with load analysis and E24 matching

Solve For

Input Voltage (Vin)

R1 (top) (kΩ)

R2 (bottom) (kΩ)

Load Resistance (optional) (kΩ)

Result

Output Voltage

—

Divider Current

—

Output Impedance

—

Power in R1

—

Power in R2

—

Vout Range (±5% R)

—

Common Presets

Features

Two modes: calculate Vout from resistors, or find R1/R2 from a target voltage Load resistance analysis — see how Rload affects actual output voltage E24 standard value matching with tolerance range (±1% and ±5%) Interactive schematic with current flow and power dissipation per resistor

FAQ

How does a voltage divider work?

Two resistors in series divide the input voltage proportionally. Vout = Vin × R2 / (R1 + R2). The output is taken from the junction between R1 and R2.

Why does adding a load change Vout?

A load resistance (Rload) appears in parallel with R2, reducing the effective R2 value. This pulls Vout lower than the unloaded calculation predicts.

What is output impedance?

Zout = R1 × R2 / (R1 + R2) — the Thevenin equivalent resistance. Lower Zout means the divider can drive loads without significant voltage drop.

How do I choose R1 and R2 values?

Use values that give the correct ratio while keeping current reasonable. Too low (e.g. 10Ω) wastes power. Too high (e.g. 10MΩ) is sensitive to noise and loading.

Can I use a voltage divider as a power supply?

No. Voltage dividers cannot regulate voltage under varying loads. Use a voltage regulator (LDO, buck converter) for power supplies. Dividers are for signal level shifting and voltage sensing.

💡 Want us to improve this tool just for you?

We can — and it's free! Just send us a quick message with your idea. If you'd like to discuss it in detail, leave your email and we'll get back to you. You can stay anonymous.

How do you rate this tool?

Thank you for your rating!

Change my rating

Want to leave a comment?

Want to share more? Leave a comment!

Thank you! Your comment will appear after moderation.

Who is this tool for?

🔌 Electronics Enthusiasts

Published 06 Apr 2026 Updated 10 Jun 2026