While there are some recommendations for the mounting height of ADA signs, there are no guidelines for the size of the accessible entrance signs, as such. Therefore, you must decide on the size based on the viewing distance and speed (if people are viewing the sign from a moving vehicle).  As a thumb rule, bigger the sign, better the readability, even from a distance. Most popular sizes for aluminum signs are 12”x 18” and 18” x 24”. The largest accessible entrance sign we offer measures 24” x 30”. Our supplemental ADA signs are 6” x 12”. Pick a size and design that will best suit your needs.