Brick and wooden raised beds filled with dark soil and young plants, on a gravel path in front of a brick cottage row. Photo via Unsplash.
How do you calculate cubic yards for a raised bed? Multiply length x width x depth in feet, then divide by 27. An 8 by 4 foot bed filled 10 inches deep is 8 x 4 x 0.833 = 26.67 cubic feet, which is 0.99 cubic yards. In bags, that is 14 bags of 2 cu ft or 18 bags of 1.5 cu ft.
The cubic yard calculator does this for you in feet and inches or meters and centimeters, and shows bag counts for common sizes. Below are the worked examples for raised beds and balcony planters, a simple soil mix, and how to decide between bags and a bulk load.
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Key takeaways
Cubic yards = length x width x depth in feet / 27.
An 8 x 4 bed at 10 inches deep is almost exactly 1 cubic yard.
Bags: divide cubic feet by the bag size printed on the bag, then round up.
A common fill is 1:1 compost and soilless mix, per University of Maryland Extension.
Beds on a hard surface need at least 8 inches for greens and 12 to 24 inches for tomatoes.
Soil settles, so buy a little extra or plan to top up after the first few waterings.
What Is the Formula for Cubic Yards?
Rectangular beds are the easiest to measure: length x width x soil depth. Photo via Unsplash.
Measure the inside length and width of the bed in feet. Use the inside, not the outside of the boards.
Measure the soil depth you want in inches and divide by 12. A 12 inch bed filled to 10 inches is 0.833 ft.
Multiply length x width x depth = cubic feet.
Divide by 27 = cubic yards. A yard is 3 feet, and 3 x 3 x 3 = 27.
In metric, multiply the three measurements in meters for cubic meters. One cubic meter is 1.308 cubic yards, or 1,000 liters.
Round planter or half barrel: use 3.1416 x radius x radius for the area. A 24 inch planter filled 16 inches deep is 3.1416 x 1 x 1 x 1.333 = 4.19 cubic feet.
How Many Cubic Yards for a 4 x 8 Raised Bed?
8 x 4 ft bed, filled 10 inches deep:
8 x 4 x 0.833 = 26.67 cubic feet
26.67 / 27 = 0.99 cubic yards (0.76 cubic meters)
14 bags of 2 cu ft, 18 bags of 1.5 cu ft, 21 bags of 1.3 cu ft, or 27 bags of 1 cu ft
Fill it to 12 inches and it becomes 32 cubic feet, or 1.19 cubic yards.
4 x 4 ft bed, 12 inches deep: 4 x 4 x 1 = 16 cubic feet, 0.59 cubic yards. That is 11 bags of 1.5 cu ft or 8 bags of 2 cu ft.
Two 8 x 4 beds at 12 inches: 64 cubic feet, 2.37 cubic yards. Many landscape yards sell soil in half-yard or whole-yard steps, so round up to 2.5 yards and ask. In 1.5 cu ft bags it is 43 bags.
How Much Soil for a Balcony Planter?
Planters are small enough that cubic yards stop being useful. Work in cubic feet or liters and count bags.
Rectangular planter, 36 x 12 inches, filled 10 inches deep:
3 x 1 x 0.833 = 2.5 cubic feet (about 71 liters)
2 bags of 1.5 cu ft (1.67 rounded up)
A pair of these planters: 5 cubic feet, 4 bags
Metric balcony box, 1.2 m x 0.6 m x 30 cm: 1.2 x 0.6 x 0.3 = 0.216 cubic meters, which is 216 liters, 7.63 cubic feet, or 0.28 cubic yards. A 1.5 cu ft bag holds about 42.5 liters, so that is 6 bags.
Wet soil is heavy. Check your lease or building rules about balcony loads before you fill several large planters, and put the heaviest ones near the wall rather than the railing. For making the balcony and living room feel like one space, see small living room ideas for apartments.
What Soil Mix Should Go in a Raised Bed?
University of Maryland Extension gives two simple recipes:
Bed on a hard surface, or a fresh start: compost and a soilless growing mix, 1:1 by volume. Topsoil can be up to 20% of the mix in beds at least 16 inches deep.
Bed on decent native soil: compost and topsoil at 1:1 or 1:2.
To split a volume into a mix, just divide. The 8 x 4 bed at 10 inches is 26.67 cubic feet, so a 1:1 mix is about 13.3 cubic feet of compost plus 13.3 of soilless mix. In 1.5 cu ft bags that is 9 bags of each.
Bagged "raised bed soil" is the ready-made version. Miracle-Gro sells it in 1.3 and 1.5 cu ft bags, so check which size is on the shelf before you count.
How deep? On a patio or balcony, the same Extension guide recommends at least 8 inches for leafy greens, beans, and cucumbers, and 12 to 24 inches for peppers, tomatoes, and squash. Michigan State University Extension puts 10 inches as the minimum for most vegetables.
Should You Buy Soil in Bags or in Bulk?
One cubic yard is 27 cubic feet, so:
Bag size
Bags per cubic yard
1 cu ft
27
1.3 cu ft
21 (20.8)
1.5 cu ft
18
2 cu ft
14 (13.5)
Bags make sense for planters, one small bed, or anything you carry up stairs. They stay clean in the car and leftover bags keep. Price bulk once you need about 2 yards or more. Ask about the delivery fee and minimum order, and where the driver can drop the pile. A pile on a shared driveway is a problem in most apartment buildings.
Here is one practical detail worth knowing. On its Home Depot listings, Miracle-Gro says two bags of its 1.5 cu ft raised bed soil fill a 2 x 2 ft bed 6 inches deep. That bed is 2 cubic feet, and two bags are 3. Bag volume is measured loose, and the soil settles once it is watered. So buy a bag or two more than the math says, or plan to top up after the first week.
How many cubic yards of soil do I need for a 4 x 8 raised bed?
At 10 inches deep, 8 x 4 x 0.833 = 26.67 cubic feet, which is 0.99 cubic yards. At 12 inches it is 32 cubic feet, or 1.19 cubic yards.
How many bags of soil fill a 4 x 8 raised bed?
At 10 inches deep the bed holds 26.67 cubic feet. That is 14 bags of 2 cu ft, 18 bags of 1.5 cu ft, or 21 bags of 1.3 cu ft. Buy one or two extra for settling.
How many square feet does a cubic yard of soil cover?
54 sq ft at 6 inches deep, about 32 sq ft at 10 inches, and 27 sq ft at 12 inches. Divide 324 by the depth in inches.
How deep should a raised bed be?
On good native soil, 6 to 12 inches of added soil works because roots can grow down. On a patio, balcony, or other hard surface, University of Maryland Extension recommends at least 8 inches for leafy greens, beans, and cucumbers, and 12 to 24 inches for peppers, tomatoes, and squash.
What soil mix should I use in a raised bed?
University of Maryland Extension suggests compost and a soilless growing mix in a 1:1 ratio, or compost and topsoil at 1:1 or 1:2 for beds on native soil. Bagged raised bed soil is a ready-made option.
Should I buy raised bed soil in bags or bulk?
Bags for planters and one small bed, especially if you carry them up stairs. A cubic yard is about 18 bags of 1.5 cu ft, so for two or more full-size beds, compare a bulk price including delivery.
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