I²C Related Calculators

Tools to determine design parameters for I²C (aka I2C or IIC).

I²C Pull-up Calculator


  • Source TI SLVA689: I2C Bus Pullup Resistor Calculation
  • According to TI SLOA013 traces on a PCB with a ground and power plane will be about 1-3 pF/in. and low capacitance cables about 20-30 pF/ft conductor to shield.
  • According to NXP UM10204 each device can add up to 10pF of bus capacitance. STM32 MCUs have a typical capacitance of 5pF per IO.
  • Low-level output current for Standard (100kb/s) and Fast (400kb/s) modes are min. 3mA, 20mA for Fast-mode Plus (1Mb/s) at 0.4V.
  • For a more detailed guide on trace capacitance see: I2C Design Mathematics: Capacitance and Resistance
  • Rise times: max. 1000, 300, 120ns for Standard, Fast, Fast+ modes respectively. Min 20ns only for Fast mode.


  • Add some power estimations, for example by providing a data size in bytes, determining the clock pulses required, then the energy to create those based on the bus capacitance and 'low' duration (resistive losses)