I²C Pull-up & UART Baud Rate Calculator
Calculate I²C pull-up resistors from bus capacitance and speed, or find the UART baud rate error for a given MCU clock frequency (ESP32, Arduino, STM32).
This calculator provides rough estimates based on simplified formulas from the I²C and UART specifications. Real-world results depend on cable length, parasitic capacitance, component tolerances, and the specific hardware (e.g. fractional baud rate generators). Always cross-check safety-critical or production circuits against your microcontroller/device datasheet.
Bus Parameters
Advanced Parameters
Recommended Pull-up Range
Rmin = (VDD − VOL) / IOLRmax = tr / (0.8473 × Cb)Common Pull-up Values
How does this tool work?
Two calculators for digital interfaces: I²C pull-up sizing based on bus capacitance/speed and UART baud rate error analysis for common clock frequencies.
I²C: calculates min./max. pull-up resistance from VDD, bus capacitance (cable + device share), and mode (Standard/Fast/Fast+). UART: finds the nearest achievable divider/BRR value for a given baud rate and clock frequency plus the resulting error percentage. Results are estimates; real circuits (cable length, parasitic capacitance, component tolerances) may vary.
Where are my data processed?
Only in your browser. Your data is not sent to any server.
The tool calculates and converts with JavaScript right on your device. Input and files are not sent to us or anyone else. You can check this yourself: load the page, disconnect from the internet, and the tool keeps working in the open tab.