If a window for light was made at the outset, its measure is the same as the width of the large drill in the Temple chamber; the remains of a window is two fingerbreadths tall by one thumb wide. The remains of a window refers to one that a person blocked up but was not able to finish blocking up. If a hole was bored by water, vermin or salt, then its minimum size is that of a fist; if one intended to use it, then its minimum size is an opening of a handbreadth and, if for light, then its minimum size is a hole made by a drill. Beis Shammai say that lattices and gratings combine to form an opening the size of a hole made by a drill; Beis Hillel say this is only when there’s a hole of the size made by the drill in one place. This conveys impurity and allows impurity to exit; Rabbi Shimon says it only conveys impurity, while allowing impurity to exit requires an opening the size of a handbreadth.
Regarding a window in the open air, its minimum size is the width of a hole made by a drill. If a house was built outside it, then its measure is an opening of a handbreadth. If one put the roof in the middle of the window, then the minimum size of the lower part is a handbreadth and the measure of the upper part is the width of a hole made by a drill.