# 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).

- Open in browser: https://pockettoolbox.org/en/i2c-uart-calculator
- Runs entirely in your browser; files and input are never uploaded.

## How it works

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.

I²C mode: Computes minimum and maximum pull-up resistance based on bus capacitance and RC rise-time limits per NXP spec. UART mode: Calculates divider values and percentage baud rate errors for a target clock frequency.

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PocketToolbox (https://pockettoolbox.org/en)