Baud Rate Calculator
A free serial communication calculator for UART, SPI, and I2C protocols. Calculate UART baud rate dividers with error percentage and reliability indicators, SPI clock speeds from system clock and divider, and I2C pull-up resistor values based on bus capacitance — with a built-in data transfer time estimator.
Protocol Mode
System Clock (MHz)
Frame Settings
Desired Baud Rate
Result
Standard Baud Rate Table
| Baud Rate | Divider | Actual Baud Rate | Error | Status |
|---|---|---|---|---|
| 9,600 | 104 | 9,615.38 | 0.16% | |
| 19,200 | 52 | 19,230.77 | 0.16% | |
| 38,400 | 26 | 38,461.54 | 0.16% | |
| 57,600 | 17 | 58,823.53 | 2.12% | |
| 115,200 | 9 | 111,111.11 | 3.55% | |
| 230,400 | 4 | 250,000 | 8.51% | |
| 460,800 | 2 | 500,000 | 8.51% | |
| 921,600 | 1 | 1,000,000 | 8.51% |
Data Transfer Time
What is a Baud Rate Calculator?
A Baud Rate Calculator helps embedded system engineers determine the correct settings for serial communication protocols. For UART, it calculates the divider register value and actual baud rate from a system clock frequency, showing the error percentage that indicates communication reliability. It also supports SPI clock calculations and I2C pull-up resistor recommendations.
How to Use the Baud Rate Calculator
- Select a protocol mode: UART, SPI, or I2C
- Enter your system clock frequency in MHz
- For UART: set the desired baud rate and frame settings to see divider and error
- For SPI: select a clock divider to see the resulting SPI clock speed
- For I2C: choose a speed mode and enter bus capacitance for pull-up resistor values
Frequently Asked Questions
What baud rate error percentage is acceptable for UART?
For reliable UART communication, the total baud rate error between sender and receiver should be less than 2%. Each side contributes to the total error, so aim for less than 1% per device. Errors above 3% typically cause frequent data corruption.
How is the UART divider calculated?
The divider is calculated as: Divider = round(System Clock / (16 × Desired Baud Rate)). The factor of 16 comes from the 16x oversampling used in most UART hardware for clock recovery and noise filtering.
What pull-up resistor should I use for I2C?
The recommended pull-up resistor depends on bus capacitance and I2C speed. For Standard mode (100 kHz) with typical capacitance (100 pF), 4.7 kΩ is common. Higher speeds require lower resistor values. Our calculator provides min, recommended, and max values based on I2C specifications.
What is the difference between baud rate and bit rate?
Baud rate measures symbol changes per second, while bit rate measures bits per second. For binary signaling (used in UART), they are the same. For multi-level signaling, bit rate = baud rate × bits per symbol.