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Raised Garden Bed Soil Calculator
Work out how much soil fills your raised garden beds, in cubic feet, cubic yards and bags, with the amount of each ingredient for a good raised bed mix and the boards to build the beds.
How much soil does a raised bed need?
Multiply the length and width in feet by the depth in inches and divide by 12 to get cubic feet. Divide by 27 for cubic yards.
cubic feet = length (ft) × width (ft) × height (in) ÷ 12
An 8 × 4 ft bed, 12 in deep, holds 32 cu ft. Two of them hold 64 cu ft, or 2.37 cu yd. In 1.5 cu ft bags that is 43 bags (about $430 at $10 a bag), while bulk soil at $45 a yard costs about $107 plus delivery. Bulk usually wins once you need more than about a cubic yard.
Common bed sizes
| Bed size | Depth | Soil |
|---|---|---|
| 4 × 4 ft | 12 in | 16 cu ft (0.59 cu yd) |
| 4 × 8 ft | 12 in | 32 cu ft (1.19 cu yd) |
| 4 × 8 ft | 18 in | 48 cu ft (1.78 cu yd) |
| 3 × 6 ft | 10 in | 15 cu ft (0.56 cu yd) |
| 4 × 12 ft | 24 in | 96 cu ft (3.56 cu yd) |
Choosing a soil mix
- 60 / 30 / 10 (topsoil, compost, perlite or pumice) is affordable for large or deep beds and holds water well. Use screened topsoil, not fill dirt.
- Mel's Mix from Square Foot Gardening is light and fluffy, great for shallow 6 in beds, but costs more per cubic foot.
- Tall beds (24 in and up) can be part-filled with logs, branches and leaves at the bottom (hugelkultur) to cut soil costs by a third or more.
Building the beds
A 2 × 6 board is actually 5½ in tall, so a 12 in bed takes three courses (16½ in) or two courses if you are fine with 11 in. Untreated cedar lasts 10 to 15 years; modern pressure-treated lumber (ACQ or CA) is considered safe for vegetable beds by most extension services, and you can line the inside with plastic if you prefer.
Filling a regular garden bed instead? Use the topsoil calculator or mulch calculator.
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
A 4 × 8 ft bed 12 in deep needs 32 cu ft of soil, about 1.2 cu yd or 22 bags of 1.5 cu ft.
What is the best soil mix for raised beds?
A common mix is 60% screened topsoil, 30% compost and 10% perlite or pumice. Mel's Mix of equal parts peat or coir, compost and vermiculite is lighter but costs more.
How deep should a raised garden bed be?
8 to 12 in suits most vegetables and herbs. Root crops like carrots and potatoes do better with 12 to 18 in.