How to calculate a raised garden bed
Raised beds are filled with a blend of soil and compost, so a small bed needs less than a full cubic yard.
- Measure the inside length, width, and soil height of each bed.
- Multiply by the number of beds with the quantity box.
- Fill to within an inch or two of the top.
- Order extra for settling in the first season.
Worked example
For a typical raised garden bed with length 8 ft, width 4 ft, depth 10 in, the volume is 26.67 cubic feet. Divide by 27 for 0.99 cubic yards. With a 10 percent allowance, plan for 1.09 cubic yards.
In garden soil, 0.99 cubic yards weighs about 0.84 US tons at a planning value of 1,700 pounds per cubic yard.
Raised Garden Bed sizes and quantities
These common sizes are calculated with the same formula as the tool above, so you can find your number quickly.
| Size | Cubic feet | Cubic yards | With 10 percent extra | US tons |
|---|---|---|---|---|
| 4 by 4 ft, 8 in | 10.67 | 0.40 | 0.43 | 0.34 |
| 8 by 4 ft, 10 in | 26.67 | 0.99 | 1.09 | 0.84 |
| 12 by 4 ft, 12 in | 48.00 | 1.78 | 1.96 | 1.51 |
| 20 by 4 ft, 12 in | 80.00 | 2.96 | 3.26 | 2.52 |
Tips
- A 4 by 8 foot bed 12 inches deep needs about 1.2 cubic yards.
- Mix about 60 percent topsoil with 30 percent compost and 10 percent drainage material.
- Bulk soil beats bags for more than three beds.
Common mistakes to avoid
- Measuring outside dimensions instead of inside.
- Skipping the extra for settling.
- Using plain topsoil with poor drainage.
These figures are planning estimates. Real material varies in moisture, size, and compaction, so confirm weights and order quantities with your supplier.
Frequently asked questions
How many cubic yards do I need for a raised garden bed?
Multiply the dimensions in feet and divide by 27. The example above, length 8 ft, width 4 ft, depth 10 in, needs 0.99 cubic yards before waste.
How much extra should I order?
Add 5 to 10 percent for waste. Add more if the ground is uneven or the material is loose.
Can I enter inches and feet together?
Yes. Each box has its own unit selector, so you can mix feet and inches.
How much does raised garden bed material weigh?
0.99 cubic yards of garden soil weighs about 0.84 US tons as a planning value.