It is given in philips i2c specification that maximum number of devices connected to the bus is limited by bus capacitance.There is formula specified for pull up resistor but there is no formula to calculate bus capacitance. Then how to calculate bus capacitance?
Each device on the I2C bus will contribute to the bus capacitance. These values are taken from the device datasheet and added together. Example taken from the first I2C device datasheet I found, the M24C08:
Remember to include the capacitance of the master device too. Maximum capacitance for the bus is 400pF.