Step 2 - Soil & Fill
Raised Bed Soil Calculator
Enter your bed dimensions. Get cubic feet, cubic yards, a bag count, and a layered plan that makes a deep bed affordable.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Filling a raised bed costs more than most people budget for, and the surprise always arrives after the bed is assembled. Work the volume out first. Enter your dimensions below and the calculator returns the total fill, the bag count at common bag sizes, and a layered plan that reduces how much of it has to be bought mix.
Work out how much soil you need
Enter the inside dimensions of your bed. Depth is how deep you intend to fill it, which is usually the full height of the bed.
35.2 cu ft
Total fill needed
includes 10% for settling
1.30 cu yd
In bulk terms
1 cu yd = 27 cu ft
32 cu ft
Per bed, before settling
length x width x depth
If you buy it in bags
| Bag size | Bags for the whole fill | Bags for the top 12 in only |
|---|---|---|
| 1 cu ft | 36 | 36 |
| 1.5 cu ft | 24 | 24 |
| 2 cu ft | 18 | 18 |
| 3 cu ft | 12 | 12 |
Figures are volume only. We do not quote prices, because prices vary by supplier and region and we have no live price data to cite -- check current prices at the retailer.
How the math works
Volume is length x width x depth, with every measurement in feet. A 4 x 8 ft bed filled to 12 inches is 4 x 8 x 1 = 32 cubic feet. At 17 inches the depth is 17 divided by 12, or about 1.42 feet, giving 45.3 cubic feet.
- 1 cubic yard = 27 cubic feet. That is the unit bulk suppliers deliver in, and the minimum order for many of them.
- Bagged mix is usually 1, 1.5 or 2 cubic feet per bag. Divide your total by the bag size to get the count.
- Allow 10 percent for settling. Fresh material compacts as it is watered in, so a bed filled exactly to the rim will be below the rim within a month.
You do not need to buy all of it
Vegetable roots live overwhelmingly in the top 10 to 12 inches of a bed. Below that, the material is doing structural and drainage work rather than growing work, which means it can be things you already have.
| Layer | Depth | Material | Cost |
|---|---|---|---|
| Bottom | 4 to 6 in on beds over 15 in | Logs, branches, woody prunings | Free |
| Middle | 4 to 8 in | Leaves, grass clippings, straw, spent potting soil | Free or cheap |
| Transition | As needed | Bulk topsoil and compost blend | Bulk delivery price |
| Growing layer | Top 10 to 12 in | Good raised bed mix or your own blend | Bagged mix price |
On a 17-inch bed that approach commonly halves the bagged-mix portion. The full method is in how to fill a raised garden bed, and the woody-base version is hugelkultur.
Bagged, bulk or both
For one bed, bagged mix is the least painful option despite costing the most per cubic foot -- you can carry it, store it and buy it in stages. For two or more beds, bulk delivery is usually far cheaper, with the caveat that a cubic yard arrives as a pile on your driveway and has to be barrowed.
A common compromise: bulk topsoil and compost for the lower layers, bagged raised bed mix for the top foot where it actually matters. For what to buy for that top layer, see the best raised bed soil.
What to buy
The products that fit the advice above, chosen by the process on our how we choose page. We have not hands-on tested them; specifications are the manufacturers’ own.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickEspoma Organic Raised Bed MixPurpose-made raised bed mix, widely stocked | The simple bagged default | 8.7 | Check price on Amazon |
| 2 |  Coast of Maine Castine Blend Raised Bed MixCompost-rich blend with castings, kelp and biochar | A bed you fill once and feed | 9.0 | Check price on Amazon |
| 3 |  FoxFarm Raised Bed Planting MixHeavier blend formulated for beds, not pots | Bed-scale FoxFarm | 8.6 | Check price on Amazon |
#ad We may earn a commission - prices are shown by Amazon, not by us
Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
Common questions
How much soil do I need for a 4x8 raised bed?
At 12 inches deep, 32 cubic feet -- about 1.2 cubic yards, or sixteen 2-cubic-foot bags. At 17 inches, about 45 cubic feet. Multiply length x width x depth in feet, and add roughly 10 percent for settling.
How many bags of soil fill a raised bed?
Divide your total cubic feet by the bag size. Bagged mix commonly comes in 1, 1.5 or 2 cubic foot bags, so a 32-cubic-foot bed needs 32 one-cubic-foot bags, 22 at 1.5 cubic feet, or 16 at 2 cubic feet.
How many cubic feet are in a cubic yard of soil?
Twenty-seven. That is the unit bulk suppliers sell in, and it is often the minimum delivery. A cubic yard fills a 4 x 8 ft bed to about 10 inches, so a 12-inch fill on that footprint needs slightly more than one yard.
Why does my raised bed soil keep sinking?
Organic matter breaks down and loses volume, so the level drops a few inches a year -- faster in the first season, and faster still if the bed was filled with woody or leafy material at the base. Top up with an inch or two of compost each spring.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.