Complete guide
Raised Bed Soil: The Complete Guide (Mix, Depth, Cost)
Everything that goes in a raised bed, in one place: a shopping list for 10 bed sizes, 9 extension-tested mix recipes, what to put in the bottom, and how to fill a deep bed for less.
The short answer
A good raised bed soil is 60 percent topsoil, 30 percent compost, and 10 percent perlite or vermiculite, filled 10 to 12 inches deep. A 4x8 bed at 10 inches holds 26.7 cubic feet, about 1 cubic yard. That works out to 11 bags of topsoil, 8 bags of compost, and 2 bags of perlite.
Try it — Raised Bed Soil Calculator
Full calculatorA 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 |
What raised bed soil is, and why the mix matters
Raised bed soil is a blend, not one product. It mixes mineral soil for body, compost for food, and a light material for air.
The mix matters because a bed is a closed box. Roots can't escape bad soil the way they can in open ground. A mix that packs hard or stays soggy will hold your plants back all season.
Each part has one job:
- Topsoil holds water and nutrients and gives roots something to grip.
- Compost feeds plants and builds soil life. It is the part you top up each year.
- Perlite or vermiculite keeps the mix loose so air and water can move.
A useful target comes from the University of Maryland Extension. A bed with garden soil should hold 25 to 50 percent organic matter by volume. The 30 percent compost share in a 60/30/10 mix sits inside that band.
How to fill a raised bed, step by step
Start with the volume. Then pick a mix. Then buy about 10 percent extra.
The volume is plain box math. Multiply length times width in feet, then times depth in feet (inches divided by 12). Divide by 27 to turn cubic feet into cubic yards.
cubic feet = length_ft x width_ft x (depth_in / 12)
cubic yards = cubic feet / 27
A 4x8 bed is 32 square feet. At 10 inches that is 32 x (10 / 12) = 26.7 cubic feet, or 0.99 cubic yards.
Next, split the volume by the recipe. At 60/30/10, the 4x8 bed needs 16 cubic feet of topsoil, 8 of compost, and 2.67 of perlite. Divide each by its bag size and round up.
Last, add about 10 percent for settling. Fresh mix sinks after the first few waterings as air pockets close. The 4x8 bed goes from 26.7 to about 29.3 cubic feet. In practice that is one more bag of topsoil and one more bag of compost.
The same math for other beds is in the table below. For the full worked example, see how much soil for a raised bed.
Shopping list for one 4x8 bed at 10 inches
- Total volume: 26.7 cu ft (0.99 cu yd, about 755 liters)
- Topsoil: 16 cu ft = 11 bags at 1.5 cu ft
- Compost: 8 cu ft = 8 bags at 1 cu ft
- Perlite or vermiculite: 2.67 cu ft = 2 bags at 2 cu ft
- Settling buffer: +10 percent = 29.3 cu ft, or 12 topsoil and 9 compost bags
Bag counts by bed size (60/30/10 mix, 10 inches deep)
Here is the calculator's shopping list for ten common bed sizes. Every row uses the 60/30/10 default blend, a 10-inch fill, and the calculator's default bag sizes: 1.5 cu ft topsoil, 1 cu ft compost, and 2 cu ft perlite.
| Bed size | Total volume | Total (liters) | Topsoil bags | Compost bags | Perlite bags | With 10% extra |
|---|---|---|---|---|---|---|
| 2x4 ft | 6.7 cu ft (0.25 cu yd) | 189 L | 3 | 2 | 1 | 7.3 cu ft |
| 3x3 ft | 7.5 cu ft (0.28 cu yd) | 212 L | 3 | 3 | 1 | 8.3 cu ft |
| 2x6 ft | 10.0 cu ft (0.37 cu yd) | 283 L | 4 | 3 | 1 | 11.0 cu ft |
| 2x8 ft | 13.3 cu ft (0.49 cu yd) | 378 L | 6 | 4 | 1 | 14.7 cu ft |
| 4x4 ft | 13.3 cu ft (0.49 cu yd) | 378 L | 6 | 4 | 1 | 14.7 cu ft |
| 3x6 ft | 15.0 cu ft (0.56 cu yd) | 425 L | 6 | 5 | 1 | 16.5 cu ft |
| 4x6 ft | 20.0 cu ft (0.74 cu yd) | 566 L | 8 | 6 | 1 | 22.0 cu ft |
| 4x8 ft | 26.7 cu ft (0.99 cu yd) | 755 L | 11 | 8 | 2 | 29.3 cu ft |
| 4x10 ft | 33.3 cu ft (1.23 cu yd) | 944 L | 14 | 10 | 2 | 36.7 cu ft |
| 4x12 ft | 40.0 cu ft (1.48 cu yd) | 1,133 L | 16 | 12 | 2 | 44.0 cu ft |
Bag counts cover the base volume. The last column is what to aim for once you add the settling buffer.
Notice the 2x8 and the 4x4. Both are 16 square feet, so both take the same soil. Footprint, not shape, sets the order.
Building at 12 inches instead? Multiply any total by 1.2. A 4x8 bed at 12 inches is 32 cubic feet, or about 1.19 cubic yards. The Raised Bed Soil Calculator redoes the bag split for any height.
Nine soil recipes from extension services, compared
There is no single "right" raised bed mix. Extension services publish several, and each fits a different situation.
The main split is between topsoil-based and soilless mixes. Topsoil-based mixes cost less and hold nutrients longer. Soilless mixes are light and drain fast, but they cost more and need more feeding.
| Source | Recipe (by volume) | Best for |
|---|---|---|
| Trowelful calculator default | 60% topsoil, 30% compost, 10% perlite or vermiculite | Most vegetable beds on open ground |
| University of Minnesota Extension | 1/2 to 2/3 topsoil, 1/3 to 1/2 plant-based compost | Beds built on a topsoil base |
| University of Maryland Extension | Compost and topsoil at 1:2 or 1:1, at least 8 in deep | Beds over poor or packed-down ground |
| University of Maryland Extension | Compost and soilless growing mix at 1:1 | Beds with no topsoil available |
| University of Maryland Extension | Compost and soilless mix 1:1, topsoil up to 20% only if the bed is 16 in or deeper | Beds on concrete or pavement |
| Utah State University Extension | Native topsoil plus 30–50% compost | Beds that reuse your own soil |
| Utah State University Extension | Equal parts compost, drainage material (coarse sand, vermiculite, pumice, or perlite), and topsoil | A homemade three-part blend |
| Iowa State University (cited by SDSU Extension) | Equal parts topsoil, peat moss or compost, and sand | A heavier, lower-cost blend |
| Mel's Mix (Square Foot Gardening Foundation) | Equal parts compost, peat moss, and coarse vermiculite | Square-foot gardens |
Sources: University of Minnesota Extension, University of Maryland Extension, Utah State University Extension, SDSU Extension, and the Square Foot Gardening Foundation.
The 60/30/10 default sits inside the Minnesota range and adds the perlite most native soils need. It is a safe first pick for a bed on open ground.
The hard-surface row is the odd one out. On concrete, Maryland Extension leans on compost and soilless mix and caps topsoil at 20 percent. A bed with no soil beneath it drains only through the mix itself, so lighter is better.
For a deeper look at the two most common recipes, see what soil mix for raised beds.
Pro tip
Read the bag, not the name. Rutgers Extension notes that bagged products sold as "garden soil," "topsoil," or "potting soil" are often all organic material, like bark, peat, coir, and compost. Only rarely do they contain real mineral soil. That is fine as the compost part of a mix. It is not a stand-in for the topsoil part.
What to put in the bottom of a raised bed
The bottom layer does one of two jobs. It either kills what is growing under the bed, or it fills space cheaply in a deep bed.
Some popular choices help. Others quietly hurt drainage. This table sorts them out.
| Material | Use it? | Why | Source |
|---|---|---|---|
| Plain cardboard (tape removed) | Yes, over lawn or weeds | Blocks light. With 2–4 in of compost on top, the grass dies in 8–12 weeks and rots in place | UMD Extension |
| Newspaper, several layers | Yes, over lawn or weeds | Works the same way as cardboard | UMD Extension |
| Loosened native soil | Yes | Rock a fork every 6–8 in without flipping the soil, so roots can grow down | UMD Extension |
| Soil from the paths | Yes | Dig the top 2–4 in from 2-ft paths to add depth for free | UMD Extension |
| Logs and large branches | Only in deep beds | Takes up space under the root zone, but sinks as the wood rots | SDSU and WSU Extension |
| Fresh wood chips | Only below the root zone | Mixed into soil, fresh wood ties up nitrogen as it breaks down | Utah State Extension |
| Tarp or weed fabric | Only to kill weeds, then remove | Lift it once the plants under it are dead, then add the fill | UMD Extension |
| Gravel or rocks | No | Makes a "perched water table" that holds water in the soil above and can rot roots | SDSU Extension |
| Bagged products with biosolids | No, for food beds | Skip sewage sludge products where you grow food | Rutgers Extension |
The gravel myth is the one to drop. SDSU Extension explains that water will not move from fine soil into a coarse layer until the soil above is soaked. So a gravel base keeps the bottom of the bed wetter, not drier.
Beds shallower than 12 inches need an open bottom. Utah State Extension says to loosen the ground 6 to 12 inches deep first, so roots can keep going into the soil below.
Filling a deep bed for less
Only the top 10 to 12 inches needs real growing mix. That is where most vegetable roots feed. Below that, cheaper fill can take up space.
The savings grow fast with height. Here is a 4x8 bed at eight heights, with the top 12 inches in growing mix and the rest in cheap fill.
| Bed height | Total volume | Growing mix (top 12 in) | Cheap fill below | Share that is fill |
|---|---|---|---|---|
| 12 in | 32.0 cu ft (1.19 cu yd) | 32.0 cu ft | 0 cu ft | 0% |
| 14 in | 37.3 cu ft (1.38 cu yd) | 32.0 cu ft | 5.3 cu ft | 14% |
| 16 in | 42.7 cu ft (1.58 cu yd) | 32.0 cu ft | 10.7 cu ft | 25% |
| 18 in | 48.0 cu ft (1.78 cu yd) | 32.0 cu ft | 16.0 cu ft | 33% |
| 20 in | 53.3 cu ft (1.98 cu yd) | 32.0 cu ft | 21.3 cu ft | 40% |
| 24 in | 64.0 cu ft (2.37 cu yd) | 32.0 cu ft | 32.0 cu ft | 50% |
| 30 in | 80.0 cu ft (2.96 cu yd) | 32.0 cu ft | 48.0 cu ft | 60% |
| 36 in | 96.0 cu ft (3.56 cu yd) | 32.0 cu ft | 64.0 cu ft | 67% |
A 24-inch bed is half cheap fill. A 36-inch bed is two-thirds. Tall beds make sense for gardeners who can't bend easily. SDSU Extension suggests 28 to 34 inches tall for full wheelchair access.
Some crops root deeper than 12 inches, though. SDSU notes that roots of some brassicas and cucurbits (the squash family) reach 18 to 24 inches. If the bed sits on concrete, give those crops more mix, not more fill. The how deep should soil be guide has depths by project.
The catch with woody fill
Logs and branches in the bottom is the hügelkultur idea (German for "mound culture"). SDSU presents a modified version as a way to use less soil in deep beds.
Washington State University Extension is more skeptical. It warns that woody mounds collapse as the wood breaks down, and beds must be rebuilt.
So treat wood as a real saving with a known cost. Keep it below the root zone. Expect the soil line to drop over the first year or two, and keep a few bags of mix on hand to top up.
If you do mix fresh wood into the soil, add nitrogen. Utah State Extension adds about 1/4 pound of actual nitrogen per 100 square feet for each inch of fresh woody material.
Bulk vs bagged: where the line is
Bagged soil is simple for one small bed. There is no delivery minimum, and you buy the exact count the calculator gives you.
Bulk wins once you pass about 1 cubic yard, which is 27 cubic feet. A single 4x8 bed at 10 inches sits right on that line. Two or more beds almost always favor bulk.
| Project | Volume | Usually cheaper |
|---|---|---|
| One 2x4 or 4x4 bed | under 1 cu yd | Bagged |
| One 4x8 bed at 10 in | about 1 cu yd | Either, it is the line |
| Two or more beds | over 1 cu yd | Bulk delivery |
Buying bulk topsoil? Maryland Extension notes topsoil sales are not regulated there. It says to ask the dealer for soil test results and where the soil came from. Good topsoil is dark and crumbly and smells earthy. Pass on soil that smells foul, feels chalky or sticky, or shows gray mottling.
Size bagged orders by cubic feet, not weight. A 40 lb bag can hold very different volumes depending on the product and how wet it is.
Two mistakes that wreck a new bed
Common mistake
Do not fill with pure compost. Compost shrinks as it breaks down, so a pure-compost bed sinks and needs constant refills. Rutgers Extension notes that most crops evolved in mineral soil, and that more than 10 percent organic matter by weight is not recommended for general garden use. Blend compost with topsoil instead.
Do not build a shallow bed on concrete. If roots can't reach the ground, the frame height is all the soil a plant gets. Maryland Extension says beds on hard surfaces need at least 8 inches for greens, beans, and cucumbers, and 12 to 24 inches for tomatoes, peppers, and squash.
Keeping the bed going after year one
A raised bed loses a little volume every year. Compost breaks down, and the soil line creeps lower.
Top it up with compost. Rutgers Extension gives a general rule for soil low in organic matter: spread 1 to 2 inches of compost and mix it into the top 6 inches. The how much compost do I need guide and the Compost Calculator turn that depth into bags.
Once the bed is full, spacing sets how much it grows. The plant spacing chart gives in-row inches and square-foot counts for 23 crops.
Put it together
A good raised bed is a 60/30/10 mix, 10 to 12 inches deep, ordered with 10 percent extra. Keep gravel out of the bottom. Fill only what sits below the root zone with cheap material, and buy bulk once you pass a yard.
Got your bed dimensions? Open the Raised Bed Soil Calculator for your exact mix and bag list.
Common questions
What is the best soil mix for a raised garden bed?
A balanced starting mix is 60 percent topsoil, 30 percent compost, and 10 percent perlite or vermiculite. University of Minnesota Extension lands in the same zone: one-half to two-thirds topsoil and one-third to one-half compost. Square-foot gardeners often use Mel's Mix instead, which is equal parts compost, peat moss, and coarse vermiculite.
Is there a difference between raised bed soil and regular soil?
Yes. Regular topsoil is mineral soil made of sand, silt, and clay. Most bagged "raised bed soil" is mostly organic matter like bark, wood fiber, peat, and compost, and often has little or no mineral soil, per University of Maryland and Rutgers Extension. A bed does best with a blend of the two.
Can I fill my raised garden bed with just soil?
You can, but mix in compost first. Utah State University Extension says to amend native topsoil with 30 to 50 percent compost by volume. Plain topsoil alone tends to pack down and drain slowly in a bed.
Can I use bagged garden soil in raised beds?
Yes. Read the label, because many bagged soils are all organic material with no mineral soil, per Rutgers Extension. They work well blended with topsoil. For food crops, skip any product that lists sewage biosolids or sludge.
How much soil do I need for a raised bed?
Multiply length times width times depth, all in feet, then divide by 27 for cubic yards. A 4x8 bed filled 10 inches deep needs about 26.7 cubic feet, or roughly 1 cubic yard. Add 10 percent for settling, which brings it to about 29.3 cubic feet.
How deep should a raised bed be?
Aim for 10 to 12 inches for a mixed vegetable garden. On a hard surface, University of Maryland Extension says leafy greens, beans, and cucumbers need at least 8 inches, while tomatoes, peppers, and squash want 12 to 24 inches.
How to fill a raised bed cheaply?
Put cheap material in the bottom and buy good mix only for the top 10 to 12 inches, where most roots feed. Logs, branches, and loosened native soil work below that. Expect woody fill to settle as it rots, so plan to top the bed up.
What should I fill the bottom of my raised garden bed with?
Over lawn, lay plain cardboard to smother the grass. Over bare ground, loosen the soil with a fork so roots can go deeper. In a very deep bed, logs and branches can fill space below the root zone. Do not use gravel or rocks.
Should I put gravel in the bottom of my raised garden bed?
No. South Dakota State University Extension says gravel creates a "perched water table." Water stays in the soil above the gravel instead of draining, which can rot roots. Let the bed sit right on loosened soil.
Why put cardboard in the bottom of a raised bed?
Cardboard smothers the grass and weeds under a new bed. University of Maryland Extension says to cover plain, tape-free cardboard with 2 to 4 inches of compost. The plants under it die in 8 to 12 weeks and rot in place, adding organic matter.
Can I put wood chips in the bottom of my raised bed?
Yes, below the root zone. Fresh wood mixed into soil ties up nitrogen as it breaks down. Utah State Extension adds about 1/4 pound of actual nitrogen per 100 square feet for each inch of fresh woody material mixed in. Wood layers also sink as they rot.
Is it cheaper to buy raised bed soil in bulk or in bags?
Once a project needs more than about 1 cubic yard, bulk delivery usually beats bagged per cubic foot. A single 4x8 bed at 10 inches sits right at that line. Two or more beds almost always tip toward bulk.
Sources
Agronomic claims in this guide are checked against these primary sources.
- Growing Vegetables in Raised Beds — University of Maryland Extension
- Soil to Fill Raised Beds — University of Maryland Extension
- Raised bed gardens — University of Minnesota Extension
- Raised Bed Gardening — Utah State University Extension
- FS1328: Soil for Raised Beds — Rutgers NJAES Cooperative Extension
- Gardening in Raised Bed and Containers in the Northern Great Plains — South Dakota State University Extension
- Hügelkultur: What Is It, and Should It Be Used in Home Gardens? — Washington State University Extension
- The Magic of Mel's Mix Soil — Square Foot Gardening Foundation
Keep reading
How Much Soil for a Raised Bed?
Length times width times height in feet, divided by 27, gives cubic yards. A 4x8 bed at 10 inches needs about 1 cubic yard. Formula, mix ratios, bag list, and a calculator.
Read →What Soil Mix for Raised Beds?
The best raised bed soil mix is 60 percent topsoil, 30 percent compost, and 10 percent aeration. Here is why each part matters, plus the per-bag amounts for a 4x8 bed.
Read →How Deep Should Soil Be? (Raised Beds, Lawns + Gardens)
Depth depends on the project. Raised beds want 6-12 inches, a new lawn wants 4-6 inches of topsoil, and containers need 12-24 inches. Full reference table and the sources behind each number.
Read →How Much Compost Do I Need?
Multiply square feet by depth in inches, divide by 324 for cubic yards of compost. Formula, worked examples, and a bagged-vs-bulk guide.
Read →Plant Spacing Chart: In-Row Inches + Square-Foot Counts
A 23-crop vegetable spacing chart with in-row inches, row spacing, and square-foot counts side by side with K-State Extension ranges, plus real plant counts for 4x4, 4x8, and 4x12 beds.
Read →