UART Baud Rate Calculator
Calculate UART frame duration, bytes per second throughput, and baud rate error percentage for common MCU clock speeds. Helps you pick the closest standard baud rate with acceptable error.
UART Baud Rate & Timing
Calculates the UBRR register value for AVR microcontrollers (Arduino, ATtiny, etc.) to achieve accurate serial communication. Even small per-bit timing errors accumulate across the frame, so staying under 1% error is critical for reliable data transmission. Use Normal mode for most applications; U2X mode doubles the divisor, giving you more precision at higher baud rates.
Dashed line = ideal sample point per bit · dot = actual sample point with this UBRR value
U2X halves the oversampling divisor — often gets a lower error at low clock speeds.
Baud rate error
-3.55%
- UBRR value
- 8
- Actual baud
- 111,111
- Clock used
- 16 MHz
Try a different clock speed or the nearest standard baud rate.
UBRR = round(F_CPU / (16 × baud) − 1) · actual baud = F_CPU / (16 × (UBRR + 1))
More MCUs