Raised Bed Soil Calculator
Work out exactly how much soil mix your raised garden bed needs — a topsoil, compost and aeration breakdown, bags, cubic yards and cost.
Your raised bed
10-12 in suits most vegetables; 12-18 in for deep-rooted crops.
Fills the bottom of a deep bed, reducing soil mix needed above it.
Totals 100%.
Loose soil mix settles after watering and time.
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Volume breakdown
35.2 cu ft total for 1 bed
Delivery & hauling
12
Wheelbarrow loads, ~3 cu ft each
Filler base planner
The short answer
A 4×8 ft raised bed filled 12 inches deep needs about 35 cubic feet of soil mix, roughly 1.3 cubic yards. Work it out precisely by finding the bed’s volume, adding 5–10% for settling, then splitting the total by your mix ratio – commonly topsoil, compost and an aeration material like perlite or vermiculite.
Soil needed by bed size
Figures below assume a 12 inch depth, no settling allowance added.
| Bed size | Depth | Volume | Cubic yards |
|---|---|---|---|
| 3×6 ft | 12 in | 18 cu ft | 0.67 |
| 4×4 ft | 12 in | 16 cu ft | 0.59 |
| 4×8 ft | 12 in | 32 cu ft | 1.19 |
| 2×8 ft | 10 in | 13.3 cu ft | 0.49 |
| 4×8 ft | 18 in | 48 cu ft | 1.78 |
Add your settling allowance and split by mix ratio to get exact bags per component.
Soil mix options compared
| 50/50 Blend | 1/3 Blend | Mel’s Mix | |
|---|---|---|---|
| Components | Topsoil, Compost | Topsoil, Compost, Aeration | Compost, Peat/Coir, Vermiculite |
| Drainage | Moderate | Good | Very good |
| Cost | Lower | Moderate | Higher |
| Best for | Larger beds, budget builds | Most vegetable beds | Square foot gardening, small beds |
How to calculate soil for a raised bed
A raised bed is a simple rectangular or circular volume, split by your mix ratio.
- Find the bed’s volume. Length × width × depth for a rectangle, or π × radius² × depth for a circle, all in feet.
- Subtract a filler base if used. A hugelkultur-style base of logs or branches reduces the soil fill depth.
- Add a settling allowance. 5–10% covers soil compacting down after watering.
- Split by mix ratio. Multiply the total by each component’s percentage – topsoil, compost, aeration material.
- Divide by bag size and round up, or convert to cubic yards for a bulk order.
Worked example
A 4×8 ft bed, 12 inches deep, using a 1/3 blend and 1.5 cu ft bags:
- Area4 × 8 = 32 sq ft
- Depth in feet12 ÷ 12 = 1 ft
- Volume32 × 1 = 32 cu ft
- Plus 10% settling35.2 cu ft
- Topsoil (33.3%)11.7 cu ft -> 8 bags
- Compost (33.3%)11.7 cu ft -> 8 bags
- Aeration (33.4%)11.8 cu ft -> 8 bags
24 bags total across all three components, or about 1.3 cubic yards if ordering each component in bulk.
Filling a raised bed: a quick checklist
- Level the baseA flat, firm base keeps the bed’s depth consistent across its footprint.
- Add a filler base for deep bedsLogs, branches or straw in the bottom third can cut soil cost significantly on tall beds.
- Line if neededLandscape fabric on the bottom can help with weed suppression on grass or weedy ground.
- Blend components before fillingMixing topsoil, compost and aeration material together first gives a more even bed than layering.
- Water in after fillingWatering settles the soil, which is why a settling allowance in your order helps.
- Top up each seasonAn inch or two of fresh compost yearly keeps fertility and volume up as soil settles.
Common mistakes
- Using plain topsoil aloneTopsoil by itself is often too dense and low in nutrients for a productive raised bed.
- Forgetting settlingLoose soil mix compacts down noticeably after the first few waterings – order a bit extra.
- Underestimating a deep bed’s volumeDoubling the depth doubles the soil needed – easy to underestimate on tall beds.
- Skipping aeration materialHeavy, compacted soil without perlite, vermiculite or coarse compost can suffocate roots.
- Buying bags for a bulk-sized jobPast about a cubic yard per component, bulk delivery is usually cheaper than dozens of bags.
- Not accounting for a filler baseForgetting to subtract filler depth leads to over-ordering soil mix on deep beds.
What this calculator assumes
Adjust your result if your project differs from these.
- An average bagged soil mix density of about 30 lb per cubic foot for the weight estimate
- Beds treated as simple rectangles or circles at a uniform depth
- Mix percentages applied evenly across the whole bed volume
- Wheelbarrow loads of about 3 cubic feet each
- Bag sizes of 1, 1.5 and 2 cubic feet
- A filler base, if used, simply reduces the effective soil-fill depth
- Prices are whatever you enter; they are not live market rates
Common questions
How much soil do I need for a raised garden bed?
Multiply the bed’s length, width and depth in feet to get cubic feet, add 5 to 10 percent for settling, then split by your mix ratio. A 4×8 ft bed at 12 inches deep needs about 35 cubic feet of soil mix, roughly 1.3 cubic yards.
What is the best soil mix for a raised bed?
A common approach is roughly equal parts topsoil, compost and an aeration material like perlite or vermiculite. A simpler 50/50 topsoil and compost blend also works well for most vegetables and flowers.
How deep should a raised garden bed be?
Most vegetables do well with 10 to 12 inches of soil depth. Deep-rooted crops like tomatoes or root vegetables benefit from 12 to 18 inches.
Can I fill the bottom of a raised bed with logs or wood to save soil?
Yes, this hugelkultur-style technique fills the lower portion of a deep bed with logs, branches or straw, which break down over time and reduce how much soil mix you need to buy.
Should I use topsoil or garden soil in a raised bed?
Plain topsoil alone is usually too dense and low in nutrients for a raised bed. Blending it with compost and an aeration material gives better drainage and fertility than topsoil by itself.
How much does a cubic yard of garden soil cover?
One cubic yard covers about 324 square feet at 1 inch deep, or about 27 square feet at 12 inches deep, since a cubic yard equals 27 cubic feet.
Do I need to add compost every year?
Raised bed soil settles and nutrients deplete over a growing season, so topping up with an inch or two of fresh compost each year is common practice to maintain fertility and volume.
What is Mel’s Mix and is it worth using?
Mel’s Mix is a square foot gardening recipe of equal parts compost, peat moss or coco coir, and vermiculite. It’s a well-drained, nutrient-rich option, though a simpler topsoil and compost blend is more budget-friendly for larger beds.
How many bags of soil do I need for a 4×8 raised bed?
A 4×8 ft bed at 12 inches deep needs about 35 cubic feet of soil mix including settling allowance, which works out to roughly 24 x 1.5 cubic foot bags total across all mix components.
How much does raised bed soil mix cost?
Cost depends on your mix ratio, local bag or bulk pricing, and bed size. Bulk delivery by the cubic yard is usually cheaper per cubic foot than buying individual bags for larger beds.
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Raised Bed Soil Estimate
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materialcalculate.com/tools/raised-bed-soil-calculator
Project
| Bed shape | — |
| Dimensions | — |
| Depth | — |
| Soil mix | — |
| Settling allowance | — |
Volume
| Total volume | — |
| Estimated weight | — |
Mix breakdown
Cost
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes rectangular or circular beds at uniform depth, and an average bagged soil density of roughly 30 lb per cubic foot. Confirm quantities with your supplier before buying.