Raised bed soil calculator
Enter the inside size of your beds and pick a soil recipe to see the total volume, how much of each ingredient to buy, and how many bags that is.
Estimates round up. Check product labels and supplier figures before ordering.
Soil for common raised bed sizes
| Bed size (inside) | Depth | Soil needed |
|---|---|---|
| 4 x 4 ft | 12 in | 16 cu ft (0.59 cu yd) |
| 4 x 8 ft | 6 in | 16 cu ft (0.59 cu yd) |
| 4 x 8 ft | 12 in | 32 cu ft (1.19 cu yd) |
| 3 x 6 ft | 18 in | 27 cu ft (1.00 cu yd) |
| 4 x 12 ft | 12 in | 48 cu ft (1.78 cu yd) |
How it's calculated
A raised bed is a box, so its soil volume is length times width times depth. The calculator converts the depth to feet, multiplies by the number of beds, and adds your settling allowance.
Cubic feet = length (ft) x width (ft) x depth (in) / 12 x number of beds x (1 + extra % / 100)
Cubic yards = cubic feet / 27
Each ingredient = cubic feet x its share of the mix
Example: two 4 x 8 ft beds filled 12 inches deep hold 64 cubic feet. With 10% extra that is 70.4 cubic feet, or about 2.61 cubic yards. A 60/40 mix needs about 42.2 cubic feet of topsoil and 28.2 cubic feet of compost. In 1.5 cubic foot bags that is 47 bags in total.
Mel's Mix, from Square Foot Gardening, is equal parts compost, peat moss and coarse vermiculite by volume. The 60/40 and 50/50 blends are common bulk orders from landscape yards. Fresh, fluffy soil settles as it is watered, which is why the extra field starts at 10%. Bulk delivery usually beats bags once you need more than about a cubic yard.
What you'll need
- Raised garden bed kit
- Raised bed soil mix
- Bagged compost
- Coarse vermiculite
- Peat moss
Common questions
How much soil do I need for a 4 x 8 raised bed?
A 4 x 8 ft bed filled 12 inches deep holds 32 cubic feet, about 1.19 cubic yards. Add about 10% for settling, so plan on roughly 35 cubic feet.
How many bags of soil fill a raised bed?
Divide the bed's cubic feet by the bag size. A 32 cubic foot bed takes 32 bags of 1 cubic foot or about 22 bags of 1.5 cubic feet.
What is the best soil mix for raised beds?
A blend of about 60% screened topsoil and 40% compost works well for most vegetables. Mel's Mix, equal parts compost, peat moss and vermiculite, is lighter and drains well but costs more.
Can I fill the bottom of a raised bed with something cheaper?
In beds deeper than about 18 inches, some gardeners fill the bottom with logs, branches or leaves to save soil. That material breaks down and settles, so expect to top up each year.