How this calculator works
Soil is the length times the width times the depth, for each bed, plus a settling allowance. A bag of raised-bed mix is usually 2 cubic feet, and a cubic yard is 27. The frame is the perimeter of each bed, divided by the board length, times the number of boards stacked to reach the depth.
Worked example: two 8 × 4 ft beds filled 12 inches deep take 70.4 cubic feet (2.6 cubic yards) of soil with 10% settling, which is 36 bags of 2 ft³. Each frame is 1 board high in 2×12 lumber, so the two beds take 6 boards of 8 ft.
Soil for one raised bed (12 in deep, 10% settling)
Soil in cubic feet and yards, bags of 2 ft³, and 8 ft boards for a 2×12 frame.
| Bed | Soil | Cubic yards | Bags of 2 ft³ | Boards |
|---|---|---|---|---|
| 4 × 4 ft | 17.6 ft³ | 0.65 | 9 | 2 |
| 3 × 6 ft | 19.8 ft³ | 0.73 | 10 | 3 |
| 4 × 8 ft | 35.2 ft³ | 1.30 | 18 | 3 |
| 4 × 12 ft | 52.8 ft³ | 1.96 | 27 | 4 |
Tips before you buy
- Fill the bottom with cheaper material such as logs or compost, topped with 8 to 10 inches of good soil, if you want to save money on a deep bed.
- Keep beds 3 to 4 feet wide, so that you can reach the middle from the edge without stepping in.
- Leave 2 to 3 feet between beds for the path, and mulch it to keep weeds down.
- Choose untreated cedar or redwood, or modern pressure-treated lumber that is approved for garden use.
- Add a drip irrigation line when you build the beds, which is far easier before they are planted.
Tools & materials for this project
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Frequently asked questions
How much soil do I need for two 4x8 raised beds?
70 cubic feet (2.6 cubic yards) at 12 inches deep, with 10% extra for settling. In bags of 2 ft³ that is 36 bags, so bulk delivery is usually cheaper.
How many boards do I need for a 4x8 raised bed?
3 boards of 8 ft make one frame 1 board high: two 8 ft sides, and one board cut in half for the 4 ft ends. A 2×12 gives about 11 inches of height.
How deep should a raised bed be?
10 to 12 inches is enough for most vegetables, and 6 inches will do for lettuce and herbs. Deeper beds suit root crops or a bed on poor ground.
How many cubic feet in a cubic yard?
27. A bag of 2 ft³ is 1/13.5 of a cubic yard, so 14 bags make about a yard.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.