How much soil do your raised beds need?
Enter your beds, get cubic feet, yards, liters and bags instantly.
Bottom fill is anything that is not soil, such as logs, branches or wood chips: the depth is taken out of the soil. No source gives a settling percentage — 10% is only an example, set your own.
How much soil do I need for a raised bed?
Multiply length × width × the depth of the soil: a 4 ft × 8 ft bed filled 12 inches deep holds 4 × 8 × 1 = 32 cubic feet, which is 1.19 cubic yards or about 906 liters. With several identical beds, multiply by how many there are. Add a little extra for settling — the extension sources we read give no percentage, so the calculator lets you pick your own.
How many bags of soil will that take?
Divide the volume by the bag size and round up. The 32 cubic feet above is 22 bags of 1.5 cubic feet, 16 bags of 2 cubic feet or 11 bags of 3 cubic feet. Sizes vary by brand: Miracle-Gro sells garden soil in 0.75, 1, 1.5 and 2 cubic foot bags and its Organic Raised Bed & Garden Soil in 1.5; Kellogg Garden's Raised Bed & Potting Mix is 2 cubic feet on the maker's site and 3 cubic feet in Home Depot and Lowe's listings. Miracle-Gro says two of its 1.5 cubic foot bags fill a 2 ft × 2 ft raised bed 6 inches deep. Check the bag for its size.
What soil mix should I put in a raised bed?
Iowa State University Extension suggests equal parts topsoil, organic matter (well-rotted manure, compost or peat) and coarse sand, or about 70% topsoil and 30% compost. The University of Maryland Extension says organic matter should be 25% to 50% of a bed with garden soil, by volume, and Utah State Extension gives a 1:1:1 mix by volume of composted organic matter, drainage material and topsoil. Mel's Mix from Mel Bartholomew's Square Foot Gardening book is equal volumes of blended compost, peat moss (or coconut coir) and coarse vermiculite. Pick one in the calculator to split your total volume between its parts.
How deep should a raised bed be?
Utah State University Extension says the box should be at least 6 to 12 inches high for the rooting depth of most vegetables. The University of Maryland Extension says a bed on a hard surface needs at least 8 inches for leafy greens, beans and cucumbers, and 12 to 24 inches for peppers, tomatoes and squash. Enter the depth of the soil, from the bottom of the bed to the soil surface.
Can I fill the bottom with something other than soil?
If you will put something coarse at the bottom of a deep bed, such as logs, branches, wood chips or stones, enter its depth under Fill the bottom with. The calculator subtracts it from the soil depth and shows its volume separately, without the settling allowance. None of the extension pages we read gives a depth for it, so that is your choice.
Sources: Iowa State University Extension, “What would be a good soil mix for a raised bed?”; University of Maryland Extension, “Soil to Fill Raised Beds”; Utah State University Extension, “Raised Bed Gardening”; Square Foot Gardening Foundation, “Method” (Mel's Mix; Mel Bartholomew, Square Foot Gardening, 1981); Scotts Miracle-Gro and Kellogg Garden product pages for bag sizes. Beds that are not raised: topsoil, compost and cubic yard calculators. How we check our calculators.