One of the greatest technique of marketing your product, cause or business is through the help of posters. If you have the right size of poster then it is a guarantee that your message would be effectively conveyed to your target audience. For this reason one of the most suitable size of a poster are the 12.75” x 17.25” posters. Due to their precise size, there is no way that they will be ignored. Secondly, you can also customize them.