Planting
Raised Bed Soil Calculator
Enter your bed dimensions to get total fill volume and a mix breakdown. Raised beds swallow far more soil than people expect, a single 4 × 8 ft bed at 12 inches deep takes nearly 32 cubic feet.
Updated
Bed dimensions
4 ft is the practical maximum, you need to reach the middle from both sides.
6 in for greens and herbs, 10–12 for most vegetables, 12+ for root crops.
Space left below the rim so watering doesn't wash soil over the sides.
Soil needed
0.99 cu yd (0.76 m³) across 1 bed
- Per bed
26.7cu ft
0.76 m³
- 1.5 cu ft (0.04 m³) bags
18
- Fill depth
10in
25.4 cm
Suggested mix
Topsoil or bulk garden soil
Compost
Aeration (bark fines, perlite, coarse sand)
Total
| Component | Share | Cubic feet | Bags |
|---|---|---|---|
| Topsoil or bulk garden soil | 60% | 16 cu ft (0.45 m³) | 16 |
| Compost | 30% | 8 cu ft (0.23 m³) | 6 |
| Aeration (bark fines, perlite, coarse sand) | 10% | 2.67 cu ft (0.08 m³) | 2 |
| Total | 100% | 26.7 cu ft (0.76 m³) |
Bagged vs bulk raised bed mix
Bagged (1.5 cu ft (0.04 m³))
Bulk delivered
| Option | Quantity | Estimated cost |
|---|---|---|
| Bagged (1.5 cu ft (0.04 m³)) | 18 bags | $180 |
| Bulk delivered | 1 cu yd (0.76 m³) | $55–$110 |
Bulk is clearly cheaper at this volume. Raised beds are where bagged soil gets expensive fast, 18 bags is a lot of plastic to haul and open.
Do not fill with straight potting mix. It is formulated for containers, costs several times more per cubic foot, and breaks down within a season or two, leaving the bed noticeably lower.
Beds settle as organic matter breaks down. Plan to top up with 1 in (2.54 cm) or 2 in (5.08 cm) of compost each spring, that is normal maintenance, not a fault.
Plan my raised bed
Tell the assistant what you want to grow and it will suggest bed depth, a soil blend, and a planting layout for the volume above.
Written by AI from the figures above. The quantities themselves are calculated deterministically and are never generated by AI. Check anything consequential, permits, utility locates, and chemical labels especially, before acting on it.
How this is calculated
Volume
Length × width × fill depth, in feet. The subtlety is fill depth versus bed depth, you do not fill to the rim. Leave about 2 inches of freeboard so watering does not wash soil over the sides.
Raised beds are where bagged soil gets expensive fast. A 4 × 8 ft bed filled 10 inches deep needs 26.7 cubic feet, which is 18 bags of 1.5 cu ft. Two beds and you are past the point where bulk delivery is cheaper even including the delivery fee.
cubic feet = length ft × width ft × (fill depth in ÷ 12)
| Bed size | Cubic feet | Cubic yards | 1.5 cu ft bags |
|---|---|---|---|
| 2 × 4 ft | 6.7 | 0.25 | 5 |
| 4 × 4 ft | 13.3 | 0.49 | 9 |
| 4 × 8 ft | 26.7 | 0.99 | 18 |
| 4 × 12 ft | 40.0 | 1.48 | 27 |
| 3 × 6 ft | 15.0 | 0.56 | 10 |
What to fill it with
A workable starting mix is roughly 60% topsoil or bulk garden soil, 30% compost, and 10% aeration material, coarse bark fines, perlite, or coarse sand. The exact ratio matters far less than avoiding the two common mistakes.
The first mistake is filling with straight bagged potting mix. It is formulated for containers, costs several times as much per cubic foot, and breaks down within a season or two, leaving the bed noticeably lower.
The second is filling with pure compost. It looks ideal and it is too rich, nutrient levels are high enough to hurt seedlings, and pure compost shrinks dramatically as it continues to decompose.
Filling deep beds cheaply
For beds deeper than about 18 inches, most plants never reach the bottom. Filling the lower third with coarse organic material, branches, logs, leaves, sometimes called hügelkultur, cuts the soil you need to buy and holds moisture as it breaks down.
Expect settling. A bed filled this way will drop noticeably over the first year as the woody material decomposes, so plan to top it up each spring.
Worked example
Two standard 4 × 8 beds
Two 4 ft × 8 ft beds, 12 inches tall, filled to 10 inches to leave freeboard.
- Fill depth
- 12 − 2 = 10 in = 0.833 ft
- Volume per bed
- 4 × 8 × 0.833 = 26.7 cu ft
- Two beds
- 53.3 cu ft
- Cubic yards
- 53.3 ÷ 27 = 1.97 cu yd
- Mix split
- 32 cu ft soil, 16 cu ft compost, 5.3 cu ft aeration
About 2 cubic yards total. Bagged that is roughly 36 bags of soil and 11 of compost, near $400. Two yards of bulk raised bed mix delivered runs $110–220, so bulk is the clear call here.
Frequently asked questions
Related calculators
Soil Calculator
Work out soil volume for any planting area, then see it costed as bags and as bulk. Handles rectangular beds, curved borders, circles, and irregular shapes built from sections.
OpenCompost Calculator
Compost gets applied far thinner than mulch or soil, and the right depth depends entirely on the job. Enter your area and pick the application to get volume, bags, and cost.
OpenTopsoil Calculator
Topsoil is heavy, roughly a ton per cubic yard, so knowing the weight matters as much as the volume. Enter your area and depth for yards, bags, and delivered tonnage.
OpenPlant Spacing Calculator
Find out how many plants a bed needs at your chosen spacing, and how many fewer you need if you offset the rows. Triangular spacing fits about 15% more plants into the same ground.
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