How to Calculate How Much Soil Is Needed in a Raised Bed Planter Box

Use a tape measure to find the length and width, in inches, of the planter box. Make your measurements on the inside of the box. Most planter boxes have sides several inches thick. If you measure the length and width on the outside, this will add considerably to your results and cause you to overestimate how much soil you need.

Measure the depth of the planter box from the bottom to the level that will be the surface. To ensure accuracy, you should first finish any excavation and leveling of the box interior before taking your measurements.

Multiply the length times the width times the depth to find the volume of soil required in cubic inches. Divide this figure by 1,728 (the number of cubic inches in one cubic foot) to convert to cubic feet. For example, if you plan a raised bed planter box 120 inches by 60 inches with a soil depth of 12 inches, you have 86,400 cubic inches. Divided by 1,728, this works out to 50 cubic feet.

Consult with a reliable lawn and garden professional (or your local agricultural extension service) to determine what type or mixture of soil you need. Different soil types have different densities. You’ll need to know what type of soil you will be using to figure the weight needed. The calculation is simple, though. Just multiply the pounds per cubic foot times the number of cubic feet to find the amount of soil needed for your raised bed planter box.