Raised Bed Soil Calculator
How much soil for your raised bed? Enter the dimensions and pick a mix — get the total plus bags of each component to buy.
A balanced, beginner-friendly mix. Good default for most vegetable beds.
Total soil needed
0.99cu yd
26.7 cu ft · buy ~29.3 cu ft to allow for settling
| Component | Volume | Bags |
|---|---|---|
| Topsoil | 16 cu ft | 11 × 1.5 cu ft |
| Compost | 8 cu ft | 8 × 1 cu ft |
| Aeration (perlite or vermiculite) | 2.7 cu ft | 2 × 2 cu ft |
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Who needs a raised bed soil calculator
This tool is for filling a new raised bed, or topping off an old one, without guessing at the volume or the mix. A raised bed's fill volume is fixed by its length, width, and depth — get the number right and you avoid ordering too little (a second trip) or too much (wasted soil and cost). The calculator also splits the total into a shopping list by component, based on whichever mix recipe you pick.
Example: a standard 4 ft × 8 ft bed filled 10 inches deep holds 4 × 8 × (10 ÷ 12) = 26.7 cubic feet, which is 26.7 ÷ 27 ≈ 0.99 cubic yards — close enough to call it 1 yard. That's the number behind the calculator's own FAQ, and it's a useful mental benchmark: a full-size 4×8 bed at a typical fill depth takes about a cubic yard of soil.
Raised bed volume by size and depth
The formula is straightforward: cubic feet = length (ft) × width (ft) × depth (ft), where depth in inches gets divided by 12 first. Divide cubic feet by 27 to get cubic yards, which is how bulk soil is usually priced and delivered. This table works it out for the bed sizes and depths gardeners ask about most, so you can look up your bed instead of doing the arithmetic.
Depth matters more than people expect: going from 6 inches to 12 inches doubles the soil you need for the same footprint, but deeper beds also drain better and give roots more room, so it's worth the extra volume for anything beyond shallow greens.
| Bed size | 6 in deep | 10 in deep | 12 in deep |
|---|---|---|---|
| 4 × 4 ft | 8 cu ft (0.30 yd) | 13.3 cu ft (0.49 yd) | 16 cu ft (0.59 yd) |
| 4 × 8 ft | 16 cu ft (0.59 yd) | 26.7 cu ft (0.99 yd) | 32 cu ft (1.19 yd) |
| 2 × 8 ft | 8 cu ft (0.30 yd) | 13.3 cu ft (0.49 yd) | 16 cu ft (0.59 yd) |
| 3 × 6 ft | 9 cu ft (0.33 yd) | 15 cu ft (0.56 yd) | 18 cu ft (0.67 yd) |
Bottom line: a 4×8 bed at a typical 10-inch fill needs about 1 cubic yard of soil — scale up or down from there for other sizes.
Mix recipes explained
A raised bed's fill is almost never a single product — pure topsoil compacts and drains poorly, and pure compost holds too much water and settles fast. The calculator's default recipe blends 60% topsoil for bulk and structure, 30% compost for fertility and organic matter, and 10% aeration material (perlite, vermiculite, or coarse sand) to keep the mix from compacting and to help roots breathe.
Mel's Mix, from the Square Foot Gardening method, is a lighter, soil-free alternative built for shallow beds and container-style growing: equal parts compost, peat moss (or coconut coir as a more sustainable substitute), and vermiculite. It drains fast and never compacts, but it holds fewer nutrients over time than a topsoil-based mix and needs more frequent feeding.
| Component | Default mix | Mel's Mix |
|---|---|---|
| Topsoil | 60% | — |
| Compost | 30% | 1/3 |
| Peat moss or coir | — | 1/3 |
| Vermiculite | — | 1/3 |
| Aeration (perlite/sand) | 10% | — |
Bottom line: the default 60/30/10 mix is cheaper and holds nutrients longer; Mel's Mix is lighter and drains faster but needs more feeding.
Filling deep beds without buying soil for all of it
A deep bed — 18 inches or more — doesn't need premium growing mix all the way to the bottom, and filling it that way gets expensive fast. Plant roots for most vegetables work mainly in the top 10–12 inches, so that's the layer worth spending on. Below that, cheaper fill does the job of taking up space and helping drainage.
Hügelkultur is one option: pack the bottom of the bed with logs, branches, and other coarse woody debris, which slowly breaks down over years and releases nutrients while improving drainage. A simpler option is just cheap fill dirt or even coarse gravel for the bottom few inches. Either way, reserve the full topsoil/compost/aeration mix for the top 10–12 inches where roots actually feed.
Bottom line: only the top 10–12 inches needs real growing mix — fill anything deeper with logs, branches, or cheap fill dirt.
Settling and buying extra
Fresh soil mix settles after it's watered in and the organic matter starts breaking down, typically dropping by around 10% in the first season as air pockets compress and compost decomposes. A bed that looked perfectly full on fill day can end up a noticeably shy of the top rail by midsummer.
Order roughly 10% more than the calculator's raw volume to cover this settling, and keep a bag or two in reserve to top off later in the season rather than ordering a small top-up separately.
How it's calculated
- 1
Enter bed size
Length, width, and fill height in inches, plus how many beds. Heights of 6–12 inches are typical.
- 2
Pick a mix recipe
The default blend is 60% topsoil, 30% compost, 10% aeration. Mel's Mix is equal parts compost, peat/coir, and vermiculite.
- 3
Get a shopping list
We split the total volume by the recipe and show bags of each component, plus a ~10% settle buffer.
Frequently asked questions
How much soil for a 4×8 raised bed?
A 4×8 bed at 10 inches deep holds about 26.7 cubic feet — roughly 1 cubic yard. The calculator breaks that into bags of topsoil, compost, and aeration.
What soil mix is best for raised beds?
A balanced default is 60% topsoil, 30% compost, 10% aeration (perlite or vermiculite). Square-foot gardeners often use Mel's Mix — equal parts compost, peat/coir, and vermiculite.
Can I fill the bottom with something cheaper?
Yes. For deep beds, the bottom 6–12 inches can be coarse fill (logs and branches — hügelkultur — or cheap fill dirt). Only the top ~10–12 inches needs real growing mix.