Quick answer: A 2×8 raised bed needs 10.67 cubic feet at 8 inches deep or 16 cubic feet at 12 inches deep. For a 12-inch fill with 5% extra, plan for 16.8 cubic feet—about 0.62 cubic yard, 12 bags at 1.5 cu ft, or 9 bags at 2 cu ft.
2×8 raised-bed soil chart
The table assumes a true 2×8-foot interior. The 5% extra is a purchasing allowance for small measurement differences and minor settling, not additional fill depth.
| Fill depth | Exact volume | Cubic yards | With 5% extra |
|---|---|---|---|
| 6 inches | 8 cu ft | 0.30 cu yd | 8.4 cu ft |
| 8 inches | 10.67 cu ft | 0.40 cu yd | 11.2 cu ft |
| 10 inches | 13.33 cu ft | 0.49 cu yd | 14.0 cu ft |
| 12 inches | 16 cu ft | 0.59 cu yd | 16.8 cu ft |
| 18 inches | 24 cu ft | 0.89 cu yd | 25.2 cu ft |
| 24 inches | 32 cu ft | 1.19 cu yd | 33.6 cu ft |
How the 2×8 calculation works
Convert the fill depth to feet, then multiply the inside length, width and depth:
2 ft × 8 ft × depth in feet = cubic feet of soil
At 12 inches deep: 2 × 8 × 1 = 16 cubic feet.
For an 8-inch fill, divide 8 by 12 first. The calculation is 2 × 8 × 0.6667, or approximately 10.67 cubic feet. Divide cubic feet by 27 to convert the result to cubic yards.
How many bags fill a 2×8 raised bed?
The purchasing quantities below include 5% extra and are rounded upward to whole bags. Check the volume on the bag because products with similar weights can contain different volumes.
| Depth | 0.75 cu ft bags | 1 cu ft bags | 1.5 cu ft bags | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|---|---|
| 6 in | 12 | 9 | 6 | 5 | 3 |
| 8 in | 15 | 12 | 8 | 6 | 4 |
| 10 in | 19 | 14 | 10 | 7 | 5 |
| 12 in | 23 | 17 | 12 | 9 | 6 |
| 18 in | 34 | 26 | 17 | 13 | 9 |
| 24 in | 45 | 34 | 23 | 17 | 12 |
Choose the real fill depth
Use the depth of the soil you will actually add rather than the height printed on the bed frame. Leaving one or two inches below the rim gives you room for watering and mulch.
Six to eight inches may work for shallow-rooted plants when the bed is open to healthy ground. Ten to twelve inches is a flexible range for many vegetables. Beds over concrete, compacted soil or a solid liner need to provide more of the complete root zone.
Example 2×8 shopping plans
2×8 bed filled 8 inches deep
Exact volume: 10.67 cubic feet. With 5% extra: 11.2 cubic feet. Buy 8 bags at 1.5 cubic feet, 6 bags at 2 cubic feet or approximately 0.42 cubic yard including the allowance.
2×8 bed filled 12 inches deep
Exact volume: 16 cubic feet. With 5% extra: 16.8 cubic feet. Buy 12 bags at 1.5 cubic feet, 9 bags at 2 cubic feet or approximately 0.62 cubic yard including the allowance.
Two 2×8 beds filled 12 inches deep
Double the single-bed total: 32 cubic feet exactly, or 33.6 cubic feet with 5% extra. That equals approximately 1.24 cubic yards including the allowance.
Why 2×8 and 4×4 beds use the same amount
A 2×8 bed and a 4×4 bed both cover 16 square feet. If their soil depths are equal, their volumes and bag counts are also equal. The long, narrow 2×8 shape may offer easier access from one side, but it does not change the amount of soil required.
Estimate the soil-mix ingredients
For a 12-inch-deep bed requiring 16 cubic feet, GardenCalcLab's 40/40/20 planning preset becomes:
- 6.4 cubic feet screened topsoil (40%)
- 6.4 cubic feet mature compost (40%)
- 3.2 cubic feet aeration material (20%)
This is a planning starting point, not a universal recipe. Adjust it for ingredient texture, compost quality, climate, crops and the soil beneath the bed.
Bagged soil or bulk soil?
Bags are convenient for one shallow 2×8 bed or locations with limited access. For deeper beds or several beds, total the complete project and compare bag costs with a delivered bulk quote, including minimum quantities and delivery fees.
Common 2×8 calculation mistakes
- Using outside dimensions: thick boards reduce the interior growing area.
- Treating inches as feet: divide the soil depth in inches by 12.
- Filling to the rim: reserve room for water and mulch.
- Rounding bags downward: always round the final bag count upward.
- Comparing bag weights: use cubic feet or liters to compare volume.
Calculate your exact bed
Change the inside measurements, soil depth, number of beds or bag size for a personalized shopping plan.
Frequently asked questions
How much soil does a 2×8 raised bed need at 12 inches deep?
A 2×8 bed filled 12 inches deep needs 16 cubic feet, or about 0.59 cubic yard. With 5% extra for minor settling and measurement differences, plan for 16.8 cubic feet.
How many bags of soil fill a 2×8 raised bed?
At 12 inches deep with 5% extra, plan for 23 bags at 0.75 cubic foot, 17 one-cubic-foot bags, 12 bags at 1.5 cubic feet, 9 bags at 2 cubic feet or 6 bags at 3 cubic feet.
Is 8 inches deep enough for a 2×8 raised bed?
Eight inches can support greens, herbs and compact crops when an open-bottomed bed sits over usable soil. Larger vegetables or a hard surface beneath the bed usually justify more depth.
Does a 2×8 bed need the same soil as a 4×4 bed?
Yes, when both use the same fill depth. Each bed covers 16 square feet, so their soil volumes are equal even though their shapes are different.