MHz
Desired Baud Actual Baud UBRR Value Error

The Baud Rate Calculator helps you calculate and compare the actual baud rate achieved with a given system clock frequency and hardware settings. It is especially useful for microcontrollers like Arduino, AVR, or other UART-based communication systems, where accurate baud rates are important for stable serial communication.

What is Baud Rate?

Baud rate is the number of signal changes (symbols) per second in a communication channel. In UART (Universal Asynchronous Receiver/Transmitter), baud rate usually matches the number of bits per second (bps). For example, a baud rate of 9600 means 9600 bits are transmitted every second.

How the Baud Rate Calculator Works

  1. Enter the system clock frequency (in MHz).
  2. Select your hardware preset (e.g., Arduino/AVR).
  3. Enable or disable double speed mode (U2X).
  4. The tool calculates the UBRR (UART Baud Rate Register) value, actual baud rate, and error percentage.
  5. You can compare multiple baud rates to see which values are accurate or have acceptable error.

Formula

The formula for calculating UBRR value depends on the mode:

  • Normal Mode: UBRR = (Fosc / (16 × Baud)) - 1
  • Double Speed Mode (U2X): UBRR = (Fosc / (8 × Baud)) - 1

Error (%) = ((Actual Baud - Desired Baud) / Desired Baud) × 100

Example Calculation

  • System Clock Frequency = 16 MHz
  • Desired Baud = 9600
  • UBRR (Normal Mode) = 103
  • Actual Baud = 9615
  • Error = 0.16%

Why Baud Rate Accuracy Matters

When the baud rate error is too high, devices may fail to communicate correctly. Errors above 3% can cause dropped data or miscommunication in most systems. Always aim for the lowest possible error percentage.

Common Baud Rates

  • 300
  • 1200
  • 2400
  • 4800
  • 9600
  • 19200
  • 38400
  • 57600
  • 115200
  • 230400
  • 250000
  • 500000
  • 1000000

FAQs

What is a safe baud rate error? Generally, an error below 2% is considered safe for reliable communication.

What is UBRR? UBRR stands for UART Baud Rate Register, which stores the calculated value used by the hardware to set the baud rate.

What happens if my baud rate is inaccurate? Communication errors, corrupted data, or complete failure to communicate may occur.

Why use double speed mode? Double speed mode (U2X) improves baud rate accuracy for some frequencies and desired baud rates.

Can I use this calculator for Arduino? Yes, it works perfectly with Arduino and AVR microcontrollers.