Free garden bed soil calculator: enter bed length, width, depth and bed count to get soil in cubic feet, cubic yards, bags and mix parts.
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Measure the inside length and width of the bed in feet (not the outside frame), enter the soil depth in inches, the number of identical beds, and your bag size. The calculator gives soil volume in cubic feet and cubic yards, whole bags rounded up, and the standard 60/30/10 mix split into topsoil, compost and perlite or coarse sand. Bulk soil is sold by the cubic yard, bagged soil by the cubic foot, so both figures are shown for shopping.
A raised bed is a box, so volume is length times width times depth, with depth converted from inches to feet by dividing by 12. A 4 × 8 foot bed filled 12 inches deep holds 4 × 8 × 1 = 32 cubic feet. Cubic yards are cubic feet divided by 27, because one cubic yard equals 27 cubic feet, so that bed needs about 1.19 cubic yards. Bags are cubic feet divided by bag size, rounded up: 32 / 1.5 = 21.3, so 22 bags of 1.5 cubic foot soil, or 16 bags of 2 cubic foot soil. The number of beds multiplies the single-bed volume.
Measure inside dimensions, because a 2 inch frame on all sides changes volume meaningfully on deep beds. Enter length, width and fill depth, not frame height: most beds want 8 to 12 inches of soil, not a full fill to the rim. Choose your bag size from the bag label, or read cubic yards if you are ordering bulk delivery. Buy roughly 10 to 15 percent extra, or plan a top-up bag, because fresh soil settles after the first few waterings.
Six inches suits shallow-rooted greens, lettuce and herbs. Twelve inches is the sweet spot for most vegetables and herbs, and the most common fill depth in competitor tables. Eighteen to 24 inches suits root crops, potatoes, tall trellised tomatoes and gardeners who prefer not to bend, but every extra inch means more soil to buy and more weight on the ground below. Deeper beds also hold moisture better in hot climates. Soil settles 10 to 15 percent in the first season, so a 12 inch fill sits near 10.5 inches after a few months. Allow for this settling when you order.
At 12 inches deep: a 2 × 4 foot bed needs 8 cubic feet (0.3 cubic yards, 6 bags of 1.5 cubic feet); a 3 × 6 foot bed needs 18 cubic feet (0.7 cubic yards, 12 bags); a 4 × 4 foot bed needs 16 cubic feet (0.6 cubic yards, 11 bags); a 4 × 8 foot bed needs 32 cubic feet (1.2 cubic yards, 22 bags); a 4 × 12 foot bed needs 48 cubic feet (1.8 cubic yards, 32 bags). At 6 inches deep, halve those figures; at 24 inches deep, double them. For beds over about 1 cubic yard, bulk delivery is usually cheaper than bags, while bags avoid a delivery minimum for a single small bed.
A common raised bed blend is 60 percent topsoil, 30 percent compost and 10 percent aeration (perlite or coarse sand). For a 4 × 8 foot bed at 12 inches, that is 19.2 cubic feet of topsoil, 9.6 of compost and 3.2 of aeration. Mel's Mix, from Mel Bartholomew Square Foot Gardening, uses equal thirds instead, a Mel's Mix ratio of 1:1:1 by volume: one third blended compost from several sources, one third peat moss or coco coir, and one third coarse vermiculite, with no topsoil at all. For the same 32 cubic foot bed, Mel's Mix is about 10.7 cubic feet of each part. Avoid pure topsoil, which packs down and drains slowly, and avoid pure compost, which settles sharply and can burn young roots.
A 4 × 8 foot bed at 12 inches deep with 1.5 cubic foot bags: volume = 4 × 8 × 1 = 32 cubic feet = 1.19 cubic yards, bags = 32 / 1.5 = 21.3, rounded up to 22 bags, mix = 19.2 topsoil, 9.6 compost, 3.2 perlite. For deep beds over 24 inches, fill the bottom third with logs, branches and leaves (hugelkultur), which decompose slowly and cut bought soil sharply. Line the bottom with cardboard to suppress weeds while letting water drain, fill in layers and water each layer so the mix settles as you go, and top up with 1 to 2 inches of compost each spring.
About 32 cubic feet at 12 inches deep, which is 1.2 cubic yards or 22 bags of 1.5 cubic foot soil. At 6 inches deep you need half that: 16 cubic feet (11 bags). Enter your exact size above for other depths.
Six inches works for shallow-rooted greens, 12 inches for most vegetables and herbs, and 18 to 24 inches for root crops and perennials like asparagus. Deeper beds hold moisture better in hot climates but cost more to fill.
Divide total cubic feet by the bag size and round up. A 32 cubic foot bed needs 22 bags of 1.5 cubic foot soil, or 16 bags of 2 cubic foot soil. Bags of 1.5 and 2 cubic feet are the common retail sizes.
27 cubic feet. A 4 × 8 × 1 foot bed is 32 cubic feet, so you would order about 1.2 cubic yards, and most bulk suppliers sell in full or half yard increments.
For beds over about 1 cubic yard, bulk delivery is usually cheaper, often 30 to 60 dollars per yard versus 5 to 8 dollars per 1.5 cubic foot bag. For small beds, bags avoid a delivery minimum and handling. Prices vary by location, so get a local quote.
A common blend is about 60 percent topsoil, 30 percent compost and 10 percent aeration (perlite or coarse sand). Pre-mixed raised bed blends work too, but check that compost makes up a good share, and avoid pure compost, which settles and can burn young roots.
Yes. Fresh soil and compost mixes settle 10 to 15 percent after the first waterings. Buy about 10 to 15 percent extra up front, or plan to top the bed off with a bag or two after a few weeks.
Not as the whole fill. In a contained bed, native garden soil compacts into a dense layer, drains poorly, and can bring weed seeds and pests. Blending up to about a third of good loam into a raised bed mix works well and cuts cost.