16 lbs. of gravel, 1/8" to 1/4" in size. Used as a supporting bed for Light to Medium density medias such as Water Softener Resin, Filter Ag & Carbon, to help insure a more even backwash. (This is enough gravel to re-bed one auto backwashing filter or water softener, with a tank diameter of 12" or less.) Gravel Specifications