The standard size for a poster board is 22 inches high and 28 inches wide. However, it is important to note that there is no official standard size for posters, and many printing and advertising companies have been using consistent sizes for poster printing over the decades. Other common poster sizes include 18x24 inches, 24x36 inches, and 27x40 inches. The size of the poster board may vary depending on the intended use, and some retailers offer variations such as tri-fold poster board measuring 36 inches high and 48 inches wide when opened.