In "Pilot", Michael robbed a bank to get himself into Fox River Penitentiary to break his brother out for a crime he did not commit. Michael hid his elaborate plan in tattoo on his body. On which body parts did he get his tattoo inked?

Michael's tattoo covers his entire upper body (torso, chest, back, arms) as an elaborate encoding of the prison blueprints and escape plan. This full upper body canvas was necessary to incorporate the complex architectural details, chemical formulas, and strategic notes required for the escape. The tattoo's comprehensive nature is why it could only be revealed gradually throughout the series.