The rule given by Vitruvius for determining the height of internal doors, and the ordinary rule when the width of the door is known, are the following. For Doric temples, the aperture of the door is determined thus: The height from the pavement to the lacunaria is to be divided into three parts and a half, of which two constitute the height of the door. The height thus obtained is to be divided into twelve parts, of which five and a half are given to the width of the bottom part of the door. This is diminished towards the top, equal to one-third of the dressing, if the height he not more than 16 ft. From 16 ft. to 25ft. the upper part of the opening is contracted one-fourth part of the dressing. From 25 ft. to 30ft. the upper part is contracted one-eighth of the dressing. Those that are higher should have their sides vertical. ... If the doors are Ionic, their height is to he regulated as in those that are Doric. Their width is found by dividing the height into two parts and a half, and taking one and a half for the width below. The diminution is to be as in the Doric doorway. ... If the doors are folding, the height remains the same, but the width is to be increased.

If in four folds the height is to be increased." Adams: Quarter height of room + 4 1/4ft. = height of door; height, of door + 4 ft. = width of door. When width of door is given the ordinary rule is to add 4 ft. for the height.