These are ballast bags rather than a base: two detachable sandbags that sit around an existing stand and take up to 90 lbs of sand, stones, soil or bottled water between them. A large opening makes filling and emptying quick, and an adjustable fixing strap holds them snug against offset and standard patio umbrella stands alike. The 900D oxford cloth carries a waterproof PU coating for wear and weather resistance. Each set measures 18.5" x 18.5" x 6.3" and weighs 1 lb empty. Two sandbags and a manual included.