Inground Winter Rectangular Swimming Pool Cover Blocks Blox Replaces Water Tubes New 1106 Swimline Winterizing Cover Block Dimensions: 36"L x 8"W x 4"H Easy to fill with sand or water Replaces standard vinyl water tubes that end up needing replaced year after year Each block is 3 feet long and should be spaced 5 feet apart. So take the circumference of your pool/8 for how many blocks you need