Within the grade stamp on a panel you will find the span rating. When there are two numbers separated by a slash (i.e. 48/24), the first number is the maximum recommended center-to-center spacing for supports in inches when the panel is used for roof sheathing with the long dimension across supports. The second number is the maximum center-to-center spacing of supports in inches when the panel is used for sub-flooring with the long dimension across supports.