Quick answer: cubic yards = length × width × depth (ft) ÷ 27. A 4 × 8 ft raised bed at 12 inches deep needs 32 ft³ ≈ 1.19 yards, or about 16 bags of 2 ft³. Order 10–15% extra, because fresh soil settles.
Soil for standard raised beds
| Bed size | 6 in deep | 12 in deep | 18 in deep | 2 ft³ bags (12 in) |
|---|---|---|---|---|
| 2 × 4 ft | 4 ft³ | 8 ft³ | 12 ft³ | 4 |
| 3 × 6 ft | 9 ft³ | 18 ft³ | 27 ft³ | 9 |
| 4 × 4 ft | 8 ft³ | 16 ft³ | 24 ft³ | 8 |
| 4 × 8 ft | 16 ft³ | 32 ft³ | 48 ft³ | 16 |
| 4 × 12 ft | 24 ft³ | 48 ft³ | 72 ft³ | 24 |
| 5 × 10 ft | 25 ft³ | 50 ft³ | 75 ft³ | 25 |
One cubic yard is 27 cubic feet, so the 4 × 8 bed at 12 inches is just under a yard and a quarter. That is the point where bulk delivery starts beating bags on price — usually by a factor of three or four once you are past a full yard.
How deep, and what to fill with
| Planting | Depth | Notes |
|---|---|---|
| New lawn / turf | 4–6 in | Over a prepared, de-compacted subgrade |
| Annual flowers | 6–8 in | Shallow roots, quick turnover |
| Vegetables (most) | 12 in | Beans, lettuce, peppers, tomatoes |
| Root crops | 12–18 in | Carrots and parsnips need loose depth |
| Perennials / shrubs | 18–24 in | Or open ground beneath the bed |
| Container / pot | Full pot | Use potting mix, not topsoil |
A common and sensible approach for deep beds is to fill the bottom third with cheaper bulk material — screened topsoil or a soil-compost blend — and reserve premium mix for the top layer where the roots actually work. That can cut the cost of a deep bed substantially without hurting anything you grow.
One caution worth repeating: bagged topsoil and bagged potting mix are different products. Topsoil compacts hard in containers and drains poorly; potting mix is far too light and expensive to fill a bed with. Pots want mix, beds want soil or a soil-compost blend.
Common mistakes & pro tips
- Depth left in inches. 4 × 8 × 12 is 384, not 32. Divide inches by 12 first, or use the unit selectors above.
- Dividing by 9 instead of 27. Nine is square yards; volume needs 27.
- Measuring the outside of the bed. Board thickness matters on small beds — a 4 × 8 bed built from 2-inch lumber has an inside footprint closer to 3.7 × 7.7 ft.
- Forgetting settlement. Compost-rich mixes can drop 10–20% in the first season. Overfill slightly and mound the centre.
- Pro tip — check what a pickup can carry. A yard of damp topsoil is over a ton. Most half-ton pickups should take one yard at a time, not the three the bed volume suggests.
- Pro tip — beds on open ground. If the bed sits on soil rather than a patio, loosen the ground underneath before filling. Roots will use that depth and you can build the bed shallower.
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
A 4 × 8 ft bed filled 12 inches deep needs 32 cubic feet, or about 1.19 cubic yards. That is roughly 16 bags of 2 cubic feet each. At 10 inches deep it drops to 26.7 ft³, just under a cubic yard.
How many bags of soil are in a cubic yard?
It depends on the bag size: 13.5 bags of 2 cubic feet, 18 bags of 1.5 cubic feet, or 27 bags of 1 cubic foot. Bagged soil costs several times more per yard than bulk delivery, so anything over about a cubic yard is usually worth ordering loose.
How deep should topsoil be?
For a new lawn, 4 to 6 inches of topsoil over the subgrade. For annual flower beds, 6 to 8 inches. For vegetable beds and deep-rooted perennials, 12 inches or more. Raised beds sitting on soil can be shallower than those on a hard surface, because roots can push into the ground beneath.
How much does a cubic yard of topsoil weigh?
About 2,160 pounds — a little over a ton — for damp screened topsoil at roughly 80 lb per cubic foot. Wet or clay-heavy soil can reach 2,700 lb per yard, which is why a single yard is about all a half-ton pickup should carry.
Should I order extra soil?
Yes, about 10 to 15 percent. Fresh soil settles noticeably in the first few weeks, especially compost-rich mixes, and beds always look underfilled once it does. Ordering a little extra is far easier than arranging a second small delivery.