The Topsoil Calculator will help you figure out how much topsoil or potting soil to buy, with an itemized breakdown in terms of bags (common sizes that you’ll find at your local hardware store) or yards (how topsoil vendors and landscapers sell it). It will convert your measurements into cubic feet and yards so you’ll know how much potting soil or topsoil you will need for your window box, garden plot, flower bed, raised garden bed, or entire yard. Just supply the length, width and depth of your project and the calculator will do the rest.
How Deep Should Topsoil Be?
Topsoil For Seeding Lawns And Sod
Both sod and grass need at least 4 inches of uncompacted, healthy soil for their roots, which grow 4-6 inches deep. How much topsoil you should add depends on the quality and compaction of your existing soil. Cornell University recommends testing your existing soil’s compaction by seeing how far a screwdriver will penetrate.
Topsoil When Covering Gravel
Because there is no existing soil, you will need a minimum of 8 to 12 inches of topsoil if you are covering a compacted surface such as gravel. The topsoil will eventually settle, so you want to allow there to still be at least 4 inches of soil once the soil has settled.
Soil For Flowerbeds And Planters
The amount of soil you need for flowerbeds also depends on the quality and compaction of your existing soil. Generally speaking, most annual flowers need 8 inches of loose, quality soil in order to develop a strong root base. Otherwise, roots will be forced to develop closer to the surface and you’ll find you have to water more because the roots dry out faster. You may be able to just top-dress the existing soil. If the existing soil is compacted, you’ll need to turn the soil so that roots will have room to grow.
The average depth of a raised garden bed is 11 inches (two 2×6 boards) and is 4 feet wide by 8 feet long. This is the minimum depth needed for vegetables such as cucumbers and tomatoes. You would need roughly 29 cubic feet of soil, which would require 39.11 .75 cu. ft. 40 pound bags of garden soil for a 4 x 8 raised garden bed at 11 inches deep.
For reference:
- One cubic yard equals 27 cubic feet.
- A 40 pound bag of topsoil usually contains about .75 Cubic Feet of soil.
- A 40 pound .75 cu. ft. bag of topsoil is enough to cover a 9 square foot area at 1 inch deep.
- There are 37.5 40 pound .75 cu. ft. bags of topsoil are in a cubic yard.
- There are 25.71404638 Dry Quarts in a Cubic Foot, so a 25 quart bag of potting soil would equal approximately 1 Cubic Foot.
