This depends on the size of your futon—or rather, the size of the "bed" it folds out into. Many futons convert into standard mattress sizes, particularly twin or full, which should be specified in the product description. In that case, you can use the appropriate sheet size. However, some are in between standard sizes, and others are smaller than a twin. If your futon is in between bedding sizes, we recommend going a size up with sheets.