In order to clear the smoke at the correct rate, the recommended free vent area you need to achieve from your window or windows is:

Stairwell Windows: 1mtr square free vent area at 90 degrees from the opening vent.

Lobby Windows: 1.5mtr square free vent area at 90 degrees from the opening vent.

Windows should be bottom hinged & open out or side hinged open out and ideally above the head of the door to clear the smoke above head height.