Then multiply by volume of stone needed by the density of the stone – which is 100 pounds per cubic foot. 140.25 feet3 x 100 pounds / foot3 = 14,025 pounds. You can see that we will need about 14,025 pounds of stone or a little over 7 tons.ixed tumbled stones weigh about 0.0618 pounds per cubic inch (or about 107 pounds per cubic foot), and we need 162 cubic inches, so we simply multiply…. 162 inches3 x 0.0619 pounds/inch3 = 10.01 pounds. There’s our answer. We need about 10 pounds of mixed tumbled stones for each planter.