Volume of a box. Soil depending on moisture content weighs in the neighborhodd of 75 to 100 pounds per cubic foot so you need to calculate the Volume total content of your box by multiplying the L in feet x W in feet x D in inches converted to feet fractions to get your total cubic feet and then multiply that by 100 use the greatest weight to get the total weight that will be on that roof. If your box is a rectangular prism or a cube the only information you need is the boxs length width and height.
The formula is then volumebox width x length x height.
To calculate the volume of soil needed to fill a regular hexagonal prism use the following formula. Multiply these numbers together to determine the volume of the box in cubic. You can put together your own raised bed planting mix using our handy calculator to figure out the right amount of each ingredient. It finds the volume according to the formulas.