Free tool
Raised Garden Bed Soil Calculator
Measure the inside of the bed, not the outside of the frame, and enter the depth you want the soil to finish at. Add a row for each bed and this totals them.
Getting the depth right
- A tall frame does not have to be soil all the way down. Filling the bottom third with coarse material and the top 12 inches with garden soil grows the same vegetables for less.
- Ten to twelve inches of good soil handles almost every home vegetable except long carrots and parsnips.
- Soil settles. Fill a little proud of the frame rather than level with it.
The maths behind it
Length times width gives square feet. Multiply that by the depth in inches, then divide by 324. The answer is cubic yards. One cubic yard covers 324 square feet at 1 inch deep, or 100 square feet at about 3¼ inches deep.
The 324 comes from a cubic yard being 27 cubic feet, and 27 times 12 inches is 324. Nothing else is going on, which is why you can check this calculator against a tape measure and a phone.
Materials this suits
Common questions
How much soil do I need for a 4 by 8 raised bed?
A 4 by 8 foot bed filled 12 inches deep needs about 1.2 cubic yards of soil, or about 1.3 cubic yards once you allow for settling. At 10 inches deep it is closer to 1 cubic yard.
How deep should a raised garden bed be?
Ten to twelve inches of soil suits nearly every home vegetable. Salad greens and herbs are happy at 8 inches. Carrots, parsnips, and potatoes do better at 12 or more.
Can I fill a raised bed with just compost?
We would not. Straight compost, including mushroom manure, is too rich and holds too much water to grow in on its own. Use a garden soil blend as the body of the bed and mix compost through the top third.
Is bulk soil cheaper than bagged soil for raised beds?
Per cubic yard, yes, and the gap widens once you are past a bed or two. One cubic yard is 27 cubic feet of soil, which is a lot of bags to carry and open. The trade-off is that bulk arrives as a pile, so you need somewhere to put it and a wheelbarrow to move it.