Raised Bed Soil Calculator: Exactly How Much Soil You Need
Guessing at soil is how you end up with three bags too many or a trip back to the store mid-project. This raised bed soil calculator gives you the exact amount, in cubic feet, cubic yards, and bags, based on your bed’s real dimensions.
Raised Bed Soil Calculator
Enter your bed dimensions and pick a soil recipe to see exactly how much you need, in cubic feet, cubic yards, and bags.
Depth is how deep you want the soil, not the full height of the bed if it has legs or a rim. Bag amounts assume standard 1.5 cu ft bags; check your product’s actual size before buying.
How the Calculator Works
The math behind it is simple: length times width times depth, all in feet, gives you cubic feet. Divide by 27 to get cubic yards, which is how bulk soil is usually sold and delivered.
A standard 4 by 8 foot bed filled 12 inches deep needs about 32 cubic feet, or roughly 1.2 cubic yards. The calculator adds a 10% cushion by default to cover natural settling, since soil compacts a little over its first season.
Pick a recipe above and the calculator also breaks the total down into topsoil, compost, and aeration material, so you know exactly how many bags of each to buy. For the full explanation behind each recipe, see our guide to raised bed soil.
Soil Depth by Crop
Not every vegetable needs the same depth. Use this as a guide when entering your own depth above.
| Rooting depth | Depth needed | Example crops |
|---|---|---|
| Shallow | 6 to 8 in | Lettuce, radishes, herbs |
| Medium | 10 to 12 in | Tomatoes, peppers, beans |
| Deep | 18 in or more | Carrots, potatoes, squash |
If your bed serves mixed crops, plan for the deepest one you are growing.
Common Bed Sizes at a Glance
Prefer a quick reference over typing in numbers? Here is what a few popular bed sizes need at a standard 12 inch depth, with the 10% settling allowance included.
| Bed size | Cubic feet | Cubic yards | Bags (1.5 cu ft) |
|---|---|---|---|
| 3 x 3 ft | 9.9 | 0.37 | 7 |
| 4 x 4 ft | 17.6 | 0.65 | 12 |
| 4 x 8 ft | 35.2 | 1.30 | 24 |
| 3 x 6 ft | 19.8 | 0.73 | 14 |
| 8 x 8 ft | 70.4 | 2.61 | 47 |
Frequently Asked Questions
How many bags of soil do I need for a 4×8 raised bed?
At a 12 inch depth with a 10% settling allowance, a 4×8 bed needs about 24 bags at the standard 1.5 cubic foot size. Check your specific product, since bag sizes vary by brand.
Why does the calculator add extra for settling?
Soil compacts naturally over its first season as organic matter breaks down and air pockets close. Adding about 10% upfront means you won’t be topping off the bed a few months in.
Can I use this for an odd-shaped bed?
This calculator is built for rectangular beds. For an L-shaped or curved bed, break the space into rectangular sections, calculate each one separately, then add the totals together.
Fill It Once, Fill It Right
Getting the volume right the first time saves you a second trip to the store and gives your plants the depth they need from day one. Enter your bed’s dimensions above, pick a recipe, and you will have your shopping list in seconds.