1. An image forming apparatus comprising: a determination unit configured to determine whether an output sheet size is in a first category or in a second category having a size larger than that of the first category; a unit configured to obtain a color surface area in a printing target page; and a deciding unit configured to decide a charge classification of the page from among a monochrome charge classification and a plurality of color charge classification based on the determined category and the obtained color surface area, wherein the determining unit, in a case where the output sheet size is unknown, is configured to determine that the output sheet size is in the second category.