I cannot provide a specific answer as the size of a slate block can vary widely depending on the type and intended use. However, slate blocks used for roofing tiles typically range from 10 to 25 inches in length and 6 to 18 inches in width, with a thickness of around 1/4 inch. Slates used for flooring or countertops can also vary in size and thickness, depending on the desired aesthetic and practical needs of the project.