A window should be of such dimensions, and in such a position, as to admit a sufficiency of light to that part of the apartment for which it is designed. No definite rule for the size can well be given that will answer in all cases; yet, as an apprpximation, the following has been used for general purposes. Multiply together the length and the breadth in feet of the apartment to be lighted, and the product by the height in feet; then the square root of this product will show the required number of square feet of glass.
For the size of window-frames, add 4 1/2 inches to the width of the glass for their width, and
6 1/2 inches to the height of the glass for their height. These give the dimensions, in the clear, of ordinary frames for 12-light windows; the height being taken at the inside edge of the sill. In a brick wall, the width of the opening is 8 inches more than the width of the glass - 4 1/2 for the stiles of the sash, and 3 1/2 for hanging stiles - and the height between the stone sill and lintel is about 10 1/2 inches more than the height of the glass, it being varied according to the thickness of the sill of the frame.