The Arduino’s I2C pins are determined by the processor. You can find the pins for the various models on the Wire library reference page . The Arduino Wire library allows you to control the I2C bus. For the Arduino Uno, the pin numbers are analog pin 4 for SDA and analog pin 5 for SCL. On the Uno rev.3 layout, SDA and SCL are also broken out on the digital side of the board, next to the ground pin.