Each long side wall of the Sistine Chapel contains six windows.
The windows are positioned high above the decorated wall surfaces, helping illuminate the chapel’s interior. Their placement was part of the building’s original architectural design rather than a later addition for Michelangelo’s ceiling project.
The chapel has two long side walls, commonly called the north and south walls because they carry different fresco cycles. The north wall presents scenes from the life of Christ, while the south wall presents scenes from the life of Moses. The windows divide these compositions and contribute to the rhythm of the interior.
A common mix-up is to count every opening in the chapel, including the entrance and altar end. This question refers specifically to the six windows along each long side wall.