These mesh bags are used in each of our AquaFalls Filters (quantity varies by size of filter), but can be used for a wide variety of other aquatic applications. 18" x 30" with drawstring top. Mesh bag shown filled with fish floss media i sold separately. This size mesh bag fits the small, medium, and large Aquafalls. Small Aquafall uses 2 mesh bags. Medium Aquafall uses 3 mesh bags. Large Aquafalls uses 6 mesh bags.