The length of the message, lettering size, and letter spacing usually determine sign size; however, several other factors can influence a sign’s dimensions. For example, the size of overhead signs may be limited by the amount of available space, particularly if the sign must be mounted over a specific lane. The size of available materials for constructing the sign may also act to limit the shape of the sign. The designer must weigh these factors in order to determine the final size of the sign; however, all previous guidelines should be adhered to.

A border should be added to all edges of the sign (typically 2 inches). Final overall sign length and height should then be adjusted from calculated measurement to the nearest multiple of 6 inches. Adjustment of overall length and height should be equally divided between the border and the nearest line of copy (Figure 4‑53). As previously mentioned, the corners of all sign borders should be rounded with a corner radius (typically 12 inches).