Work out exactly how much soil your garden beds need. Enter shape, size and depth to get cubic feet, cubic yards and bag counts instantly.
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Soil volume is pure geometry: area times depth. Pick the shape that matches your bed: rectangle uses length times width, circle uses 3.14159 times the radius squared (enter the diameter and the calculator halves it), and square planter uses side squared. Depth is entered in inches and converted to feet by dividing by 12, so all units agree before the math runs. Dividing the resulting cubic feet by 27 gives cubic yards, the unit bulk suppliers quote and deliver. Cubic feet divided by your bag size and rounded up gives the bag count for a store run. Shape convention: rectangle needs bed_length and bed_width; circle needs bed_diameter (the radius is derived as diameter / 2, so never enter a radius); square planter needs planter_side. Fields for the other shapes are ignored. Because volume scales linearly with depth, doubling the depth exactly doubles the soil volume and the cost.
Soil is sold by volume, so the math is area times depth. The calculator first works out the bed area in square feet from the shape you pick: length times width for a rectangle, 3.14159 times the radius squared for a circle, or side squared for a square planter. It converts your depth from inches to feet (depth / 12) and multiplies by the area to get the soil volume in cubic feet. It then divides by 27 for cubic yards, because one cubic yard equals 27 cubic feet and bulk suppliers price by the yard. Finally it divides the cubic feet by your chosen bag size and rounds up, since stores do not sell fractions of a bag.
Measure the inside of your bed, not the outside of the frame, since frame boards eat into the volume on deep beds. For a rectangle, measure the length and width in feet; for a circular bed, measure the diameter in feet; for a square planter, measure one side. Enter the soil depth you actually want in inches, not the height of the bed frame, then pick the bag size printed on the bags you will buy (0.75, 1, 1.5 or 2 cubic feet). The calculator updates instantly: cubic feet for bag math, cubic yards for bulk ordering, and the bag count for the store run. Only the fields matching your selected shape are used.
Depth is the number people get wrong most often, so match it to what you are growing. Herbs, lettuce and other shallow-rooted greens do fine with 6 to 8 inches of soil. Most vegetables, including tomatoes, peppers, beans and squash, want 10 to 12 inches. Deep-rooted crops like carrots, parsnips and potatoes prefer 18 to 24 inches. If you are only refreshing an existing bed, 2 to 4 inches of fresh mix each season is enough. Fill beds only to the depth your crops need, not the full height of the frame: a tall bed on open ground does not need soil to the rim because roots grow into the soil below. Fresh soil settles 10 to 15 percent after the first watering, so fill to the top and plan a top-up later.
For small jobs under about one cubic yard, bagged soil wins on convenience: no delivery minimum, easy car transport, and you buy exactly the number of bags the calculator gives you. Above one to two cubic yards, bulk soil delivered by the truckload is almost always cheaper per cubic foot, and prices per yard drop sharply. Compare price per cubic foot, not per bag, when shopping different bag sizes. Remember that one cubic yard equals 36 of the 0.75 cu ft bags, 27 of the 1 cu ft bags, 18 of the 1.5 cu ft bags, or 14 of the 2 cu ft bags, so bag costs add up fast on big beds. Order about 10 percent extra, since soil settles naturally but surplus bulk soil cannot be returned.
Take a rectangular raised bed 8 feet long and 4 feet wide, filled 8 inches deep with bagged soil in 1.5 cubic foot bags. First convert depth: 8 / 12 = 0.667 feet. Volume in cubic feet: 8 × 4 × 0.667 = 21.33 cubic feet. In cubic yards: 21.33 / 27 = 0.79 yards. In bags: 21.33 / 1.5 = 14.22, and since you cannot buy a fraction of a bag, round up to 15 bags. That is the same math the calculator runs for any shape, any depth.
This soil depth guide covers the most common raised bed depths. Salad greens and herbs grow fine in 6 inches of soil. Carrots, peppers and most vegetables need 10 to 12 inches. Root crops like potatoes and parsnips want 18 inches or deeper. Whatever the depth, fill beds to within 2 inches of the rim so watering does not wash soil out.
For a standard 4 ft by 8 ft bed filled 12 inches deep, multiply 4 × 8 × 1 = 32 cubic feet, which is 32 / 27 = 1.19 cubic yards. In bags that is 32 / 1.5 = 21.3, so buy 22 bags of 1.5 cubic foot soil. At 6 inches deep you need half that: 16 cubic feet, or about 11 bags.
One cubic yard equals 27 cubic feet, which works out to 36 small 0.75 cu ft bags, 27 one-cubic-foot bags, 18 bags of 1.5 cu ft, or 14 bags of 2 cu ft. Always round up to the next whole bag, since stores do not sell fractions.
Match depth to your plants. Shallow-rooted herbs and greens need 6 to 8 inches; most vegetables want 10 to 12 inches; deep-rooted crops like carrots and potatoes prefer 18 to 24 inches. To refresh an existing bed, add just 2 to 4 inches of fresh mix each season. Fill only the depth your crops need, not the full height of the frame.
Screened topsoil weighs roughly 2,000 to 2,200 pounds per cubic yard, which is about 1 to 1.1 US tons. Garden soil and blends run 1,800 to 2,200 pounds per yard; compost is lighter at 1,000 to 1,400 pounds, and potting mix lighter still. Weight varies with moisture: wet soil can run 20 to 50 percent heavier than dry, so check your pickup's payload before hauling bulk yourself.
A 2 cubic foot bag covers about 12 square feet at 2 inches deep, 8 square feet at 3 inches, and 6 square feet at 4 inches. A 1.5 cu ft bag covers 9, 6 and 4.5 square feet at those same depths. The general rule is coverage (sq ft) = bag volume (cu ft) / (depth in feet).
For jobs under about one cubic yard, bags are easier: no delivery minimum and you buy exactly what you need. Once you pass one to two cubic yards, bulk delivery by the yard is usually much cheaper per cubic foot. Compare the price per cubic foot, not per bag, and factor in any delivery fee before you decide.
A common and reliable blend is about 50 percent quality soil, 30 percent compost and 20 percent potting mix or aeration material like coconut coir or perlite. The classic 60 percent topsoil, 30 percent compost, 10 percent aeration also works well. Avoid filling a bed with 100 percent topsoil, which compacts, or 100 percent compost, which settles and can burn young roots.
Yes. Loose soil compresses by 10 to 15 percent after watering and settling, so a bed filled exactly to your target depth will sit below it after the first rain. Either fill to the top of the frame and let it settle, or add about 10 percent to your calculated volume for a top-up later.
To calculate soil for a garden bed, multiply length × width × depth in feet to get cubic feet, then divide by 27 for cubic yards. A 4x8 ft bed 12 inches deep needs about 1.19 cubic yards. Enter your bed dimensions above and the calculator does the conversion automatically, including a soil depth guide for common vegetables.
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