Free Raised Bed Soil Calculator
Use this raised bed soil calculator to see how much soil and compost you need to fill your raised garden beds.
A raised bed needs enough soil to fill its inside length × width × height. Enter each bed size and how many of that size you have; the calculator adds them up and splits the total into topsoil and compost.
A common mix is about 60% topsoil and 40% compost. Change the split to match your recipe; for very deep beds, some gardeners fill the bottom with cheaper fill and use the mix only for the top 12 inches.
How much soil do I need for a raised bed? An example
Two 8 × 4 ft raised beds, 12 in deep: 64 sq ft × 12 in ÷ 12 = 64 cu ft, plus 10% extra = 70.4 cu ft. Divide by 27 to get 2.61 cubic yards, which weighs about 2.22 tons, or 36 × 2 cu ft bags.
How deep should a raised bed be?
| Use | Bed height (fill depth) | Notes |
|---|---|---|
| Lettuce, herbs, shallow-rooted crops | 6 to 8 in | |
| Most vegetables | 11 to 12 in | A common height for kit beds. |
| Root crops (carrots, parsnips) and tomatoes | 12 to 18 in | |
| Tall beds for easy reach | 24 in or more | Consider filling the bottom with cheaper material. |
Soil needed for common raised bed sizes
| Bed (inside) | Height | Cubic feet | Cubic yards | 1.5 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 12 in | 16 | 0.59 | 11 |
| 4 × 8 ft | 6 in | 16 | 0.59 | 11 |
| 4 × 8 ft | 11 in | 29.3 | 1.09 | 20 |
| 4 × 8 ft | 12 in | 32 | 1.19 | 22 |
| 3 × 6 ft | 12 in | 18 | 0.67 | 12 |
| 4 × 12 ft | 12 in | 48 | 1.78 | 32 |
Coverage per cubic yard and per bag
| Bed height (fill depth) | Sq ft per cubic yard | Sq ft per 2 cu ft bag |
|---|---|---|
| 1 in | 324 | 24 |
| 2 in | 162 | 12 |
| 3 in | 108 | 8 |
| 4 in | 81 | 6 |
| 6 in | 54 | 4 |
| 8 in | 41 | 3 |
| 11 in | 29 | 2.2 |
| 12 in | 27 | 2 |
| 18 in | 18 | 1.3 |
Buying tips
- Above about one cubic yard (27 one-foot bags), buying a bulk "raised bed mix" or "garden mix" is usually cheaper than bags.
- Measure inside the bed walls. With thick timber, the inside is several inches smaller than the outside.
- Do not use fill dirt or plain clay soil in raised beds; it compacts and drains poorly.
- Top up with an inch or two of compost each year as the soil settles and breaks down.
How much does soil weigh?
A cubic yard of soil typically weighs 1,400 to 2,000 lb (0.7 to 1 tons). The calculator uses 1,700 lb (0.85 tons) per cubic yard. Moisture and grading change the weight, so if your supplier sells by the ton, ask for their figure.
Frequently asked questions
How much soil do I need for a raised bed?
Multiply the inside length × width × height in feet. A 4 × 8 ft bed 12 in deep needs 32 cubic feet, about 1.2 cubic yards, before allowing for settling.
How many bags of soil for a 4 × 8 raised bed?
For a 12 in deep bed: 32 cu ft, so 22 bags of 1.5 cu ft or 16 bags of 2 cu ft, plus a few extra for settling.
What is the best soil mix for raised beds?
Many gardeners use about 60% topsoil and 40% compost. Some add a little coarse material for drainage. Avoid heavy clay and fill dirt.
Can I use this as a raised garden bed soil calculator for several beds?
Yes. Set the quantity for each bed size, or add another area for a different size. The total covers all of them.
How accurate is this raised bed soil calculator?
The raised bed soil calculator gives the exact volume for the measurements you enter, then adds 10% extra (you can change it). Weights use a typical 0.85 tons per cubic yard; real loads vary with moisture, so confirm with your supplier if you buy by the ton. Measure carefully: an error of one inch in depth changes a 3 inch layer by a third.
How the raised bed soil calculator works
Volume = area × bed height (fill depth). Each area is worked out from its shape (length × width, π × radius², or ½ × base × height), converted to square feet, multiplied by the bed height (fill depth) in feet, and added up. Cubic feet ÷ 27 = cubic yards.The extra percentage is then added, and bag counts are rounded up to whole bags. See how we calculate for every figure we use.