When we draw a dimension from or to an outside wall, that dimension always travels to the outer edge (green dimension). When we size an inside wall, we usually assign the dimension to the wall's midline (purple). For us, the distances are more important than the actual sizes of the rooms. We know how far apart doors are expected to be from one another and from the walls. The basic dimensions of a room are height, width, and length. Height is the distance between the top of the room and the ceiling. Width is the distance between the right side of the room and the left side of the room. Length is the distance from front to back of the room. You can also measure angles: height is also called headroom because you need space above your head to walk in the room; likewise, footspace is the amount of space below your feet. Width and length are also called room parameters because they describe the size of the room. You can figure out the dimensions of a room by using mathematics and physics. The first thing to do is estimate the total volume of the room. This is easy if it is a box-like shape; otherwise, you will have to make some assumptions. Next, divide the estimated volume by the number of square feet in a square meter. This gives you the size of the room in square meters (m2). Finally, multiply this by 1,000 to get the size of the room in square feet (ft2).