How the calculator works
Enter the inside measurements of the bed and the depth of soil you want. The calculator works in feet and converts metric at the edges.
- Rectangular bed: length × width × depth, all in feet. A 10-inch depth is 10 ÷ 12 = 0.83 ft.
- Round bed: π × (diameter ÷ 2)² × depth.
- Several beds: one bed's volume × the number of beds.
- Settling allowance: the total is increased by the percentage you choose, 10% by default.
- Cubic yards = cubic feet ÷ 27. Liters = cubic feet × 28.32.
- Bags = soil to buy ÷ bag size, rounded up to whole bags.
The mix breakdown splits the total by the ratio you choose and counts bags for each part separately. Each part is rounded up on its own, so buying the parts separately can take a bag or two more than one premixed product.
Raised bed soil chart
Soil to fill common bed sizes level to the top, with no settling allowance.
| Bed size | 6 in deep | 8 in deep | 10 in deep | 12 in deep |
|---|---|---|---|---|
| 4 × 4 ft | 8 cu ft (0.3 cu yd) | 10.7 cu ft (0.4 cu yd) | 13.3 cu ft (0.49 cu yd) | 16 cu ft (0.59 cu yd) |
| 4 × 8 ft | 16 cu ft (0.59 cu yd) | 21.3 cu ft (0.79 cu yd) | 26.7 cu ft (0.99 cu yd) | 32 cu ft (1.19 cu yd) |
| 3 × 6 ft | 9 cu ft (0.33 cu yd) | 12 cu ft (0.44 cu yd) | 15 cu ft (0.56 cu yd) | 18 cu ft (0.67 cu yd) |
| 2 × 8 ft | 8 cu ft (0.3 cu yd) | 10.7 cu ft (0.4 cu yd) | 13.3 cu ft (0.49 cu yd) | 16 cu ft (0.59 cu yd) |
Bags for one 4 × 8 ft bed
With 10% extra for settling.
| Depth | Soil to buy | 0.75 cu ft bags | 1 cu ft bags | 1.5 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|---|
| 6 in | 17.6 cu ft | 24 | 18 | 12 | 9 |
| 8 in | 23.5 cu ft | 32 | 24 | 16 | 12 |
| 10 in | 29.3 cu ft | 40 | 30 | 20 | 15 |
| 12 in | 35.2 cu ft | 47 | 36 | 24 | 18 |
Example: two 4 × 8 ft beds, 10 inches deep
You are filling two 4 × 8 ft beds with 10 inches of soil, using the 60/30/10 mix and 1.5 cu ft bags.
- One bed: 4 × 8 × (10 ÷ 12) = 26.7 cubic feet.
- Two beds: 26.7 × 2 = 53.3 cubic feet.
- Settling: 10% of 53.3 is 5.3, so buy 58.7 cubic feet. That is 2.17 cubic yards, or about 1,661 liters.
- The mix: 60% topsoil is 35.2 cu ft, 30% compost is 17.6 cu ft and 10% potting mix is 5.9 cu ft.
- Bags: 35.2 ÷ 1.5 rounds up to 24 bags of topsoil, 17.6 ÷ 1.5 to 12 bags of compost and 5.9 ÷ 1.5 to 4 bags of potting mix. That is 40 bags in all.
At over 2 cubic yards, a delivered load of blended garden soil from a landscape supplier may cost less than 40 bags and saves the hauling, so compare the local prices.
Tips
- Measure the inside. Lumber sold as 2-by is 1 ½ inches thick, so a bed that is 4 × 8 ft on the outside is about 45 × 93 inches inside. A 2×12 board is 11 ¼ inches tall, and the soil usually sits an inch or so below the rim.
- Mix in layers. Spread a few inches of each ingredient in the bed, fork them together, then add the next layer. That is far easier than mixing 50 cubic feet on a tarp.
- Water before you plant. Soak the new bed and let it settle for a few days. Then top it up before you sow seeds.
- Top up every year. Spread an inch or two of compost each spring rather than replacing the soil. The bed only needs a full refill if it has a disease problem.
- Read the bag. "Garden soil" is meant to be mixed into the ground, "potting mix" is for containers, and "raised bed mix" is meant to be used on its own. Check the volume on the bag, because 1.5 and 2 cu ft bags often sit side by side on the shelf.
Frequently asked questions
How much soil do I need for a 4×8 raised bed?
A 4 × 8 ft bed filled 12 inches deep holds 32 cubic feet (1.19 cubic yards). With 10% extra for settling, buy 35.2 cubic feet, which is 24 bags of 1.5 cu ft or 18 bags of 2 cu ft. At 6 inches deep it holds 16 cubic feet.
How many bags of soil do I need for a 4×4 raised bed?
A 4 × 4 ft bed 12 inches deep holds 16 cubic feet. With 10% for settling that is 17.6 cubic feet, or 12 bags of 1.5 cu ft, 9 bags of 2 cu ft, or 18 bags of 1 cu ft. At 6 inches deep you need 6 bags of 1.5 cu ft.
What is the best soil mix for a raised bed?
A common mix is 60% topsoil, 30% compost and 10% potting mix. Equal parts topsoil and compost also works well. Square foot gardeners use Mel's Mix, equal thirds of compost, peat moss or coco coir, and coarse vermiculite. Avoid filling a bed with heavy clay alone, or with straight compost, which shrinks a lot as it breaks down.
How deep should a raised bed be?
10 to 12 inches suits most vegetables. Lettuce, spinach, radishes and herbs grow in 6 to 8 inches, especially if the ground under the bed is loosened. Long carrots, parsnips and potatoes like 12 inches or more, and on hardpan or a patio go to 18 inches.
How much does soil settle in a raised bed?
A fresh, fluffy mix with plenty of compost sinks noticeably in the first season as it is watered in and the organic matter breaks down. Many gardeners buy 10 to 20% extra, or fill to the top and add compost the next spring. The calculator adds 10% unless you change it.
What can I put in the bottom of a raised bed to save soil?
In beds deeper than about 18 inches you can fill the bottom third with untreated logs, branches and leaves, then cover them with soil. The wood breaks down over a few years, so the bed will sink more and need topping up. Over grass, a layer of plain cardboard smothers the turf.
Last updated October 17, 2026.