Quick answer: At 12 inches deep, a 2×4 bed needs 8 cu ft, a 2×8 or 4×4 needs 16 cu ft, and a 4×8 needs 32 cu ft. Soil volume equals inside length × inside width × actual fill depth.
Raised-bed soil chart by size and depth
Every figure below is the exact soil volume in cubic feet. Measure the usable inside dimensions of the bed, and use the depth you will actually fill—not necessarily the full frame height.
| Bed size | 6 in deep | 8 in deep | 10 in deep | 12 in deep | 18 in deep | 24 in deep |
|---|---|---|---|---|---|---|
| 2×4 ft | 4 cu ft | 5.33 cu ft | 6.67 cu ft | 8 cu ft | 12 cu ft | 16 cu ft |
| 2×8 ft | 8 cu ft | 10.67 cu ft | 13.33 cu ft | 16 cu ft | 24 cu ft | 32 cu ft |
| 4×4 ft | 8 cu ft | 10.67 cu ft | 13.33 cu ft | 16 cu ft | 24 cu ft | 32 cu ft |
| 4×8 ft | 16 cu ft | 21.33 cu ft | 26.67 cu ft | 32 cu ft | 48 cu ft | 64 cu ft |
To convert cubic feet to cubic yards, divide by 27. For purchasing, add your preferred allowance after totaling every bed, then round bag quantities up to the next whole bag.
Choose your raised-bed size
These quick summaries use a 12-inch fill depth. The bag count includes 5% extra and assumes 1.5-cubic-foot bags.
8 sq ft
2×4 raised bed
- Exact volume
- 8 cu ft
- Cubic yards
- 0.30 cu yd
- 1.5 cu ft bags + 5%
- 6 bags
16 sq ft
2×8 raised bed
- Exact volume
- 16 cu ft
- Cubic yards
- 0.59 cu yd
- 1.5 cu ft bags + 5%
- 12 bags
16 sq ft
4×4 raised bed
- Exact volume
- 16 cu ft
- Cubic yards
- 0.59 cu yd
- 1.5 cu ft bags + 5%
- 12 bags
32 sq ft
4×8 raised bed
- Exact volume
- 32 cu ft
- Cubic yards
- 1.19 cu yd
- 1.5 cu ft bags + 5%
- 23 bags
How to use the chart
- Measure the inside dimensions. Thick boards and liners can make the usable growing area smaller than the advertised outside size.
- Choose the actual fill depth. Leave room below the rim for watering and mulch when appropriate.
- Read the cubic-foot total. Add all beds before converting to bags or cubic yards.
- Add a purchasing allowance. Multiply by 1.05 for 5% extra or 1.10 for 10% extra.
- Round bags upward. Divide the adjusted total by the volume printed on one bag, then buy the next whole bag.
Example: Two 4×4 beds filled 12 inches deep need 32 cubic feet exactly. With 5% extra, plan for 33.6 cubic feet—23 bags at 1.5 cubic feet each, or about 1.24 cubic yards.
Why 2×8 and 4×4 beds use the same amount
Both beds cover 16 square feet: 2 × 8 = 16 and 4 × 4 = 16. At the same fill depth, their soil volumes are identical even though their shapes differ. Their layout and reach may affect garden planning, but not the amount of soil required.
Choose a practical soil depth
Six to eight inches can suit shallow-rooted crops when an open-bottomed bed sits over usable soil. Ten to twelve inches is a versatile range for many vegetables. Deeper beds may be appropriate over concrete, compacted subsoil or a solid base, or when growing crops that need a larger root zone.
Depth affects the purchase faster than many people expect. Doubling a 4×8 bed from 12 to 24 inches doubles the exact soil requirement from 32 to 64 cubic feet. Read the raised-bed soil depth guide before paying for depth you may not need.
Plan bags, bulk soil and ingredients
Bagged soil can be convenient for small projects and difficult-access areas. For larger or multiple beds, compare it with a delivered bulk quote. One cubic yard equals 27 cubic feet, but suppliers may have minimum orders and delivery charges.
After finding the total volume, choose ingredients suited to the site rather than filling the bed with one material by default. Our raised-bed soil mix guide explains a practical starting blend, while the compost calculator guide helps estimate the compost portion separately.
Calculate any bed size
Enter custom dimensions, circles, multiple beds, bag size, allowance and price for an instant shopping plan.
Frequently asked questions
How do I calculate soil for a raised bed?
Multiply the bed's inside length by its inside width by the soil depth in feet. The result is cubic feet. Divide by 27 to convert cubic feet to cubic yards.
How much extra soil should I buy for a raised bed?
A 5% allowance is a practical starting point for small measurement differences and minor settling. Use 10% when dimensions are uncertain or the soil mix is especially loose, but avoid treating the allowance as extra fill depth.
Should I use the frame height as the soil depth?
Not automatically. Measure the depth you will actually fill. Many gardeners leave one or two inches below the rim for watering and mulch, and open-bottomed beds may use suitable soil below the frame as part of the root zone.
When is bulk soil better than bags?
Bulk delivery is worth comparing once the project approaches a cubic yard, especially for multiple beds. Compare the delivered total, minimum order, soil quality, access and handling—not only the advertised price.