How to use this calculator
Two modes, because filling a raised bed and topping up a lawn are different problems.
Ground-level bed or lawn — enter the area and how deep the soil layer needs to be. Split irregular beds into rectangles and add a section for each.
Raised bed — enter the inside dimensions and the fill depth, plus how many identical beds you are filling. Use the fill depth, not the height of the sides: leaving an inch or two below the rim stops soil washing over the edge every time you water.
Bagged garden soil is more often sold in 1.5 cu ft than the 2 cu ft that is standard for mulch, so check the bag before you trust the bag count.
The formula
ground-level: volume (cu ft) = area (sq ft) × depth (in) ÷ 12
raised bed: volume (cu ft) = length (ft) × width (ft) × fill depth (in) ÷ 12 × number of beds
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size, rounded up
Worked example — one 4 ft × 8 ft raised bed, filled 12 inches deep:
- Volume: 4 × 8 × (12 ÷ 12) = 32 cubic feet
- In cubic yards: 32 ÷ 27 = 1.19 cubic yards
- In 1.5 cu ft bags: 32 ÷ 1.5 = 21.3, so 22 bags
Twenty-two bags is around 700 lb of soil to buy, transport, carry and empty for one bed. Two beds and you are past the point where a bulk delivery is both cheaper and less work.
Bags per cubic yard
| Bag size | Bags per cubic yard |
|---|---|
| 1.5 cu ft | 18 |
| 2 cu ft | 13.5 |
| 3 cu ft | 9 |
How deep
| Depth | Use |
|---|---|
| ¼–½ in | Top-dressing an established lawn |
| 2 in | Amending an existing bed |
| 4–6 in | New lawn, or a new planting bed |
| 10–12 in | Working depth for vegetables in a raised bed |
Two of these are worth dwelling on.
Top-dressing a lawn is the one people get wrong by an order of magnitude. You want a quarter to a half inch, brushed in so the grass blades still show through. An inch of soil spread over a lawn does not feed it; it smothers it.
Raised beds do not need to be filled to the top with bought garden soil. Most vegetables do their work in the top 12 inches, so filling a 24-inch bed entirely with purchased soil is money spent below the root zone. A common approach is to fill the lower half with coarse organic material, branches, or cheaper screened fill and reserve the good stuff for the top. This calculator gives you the volume for whatever depth you enter — so enter the depth you are actually buying for.
Topsoil, garden soil and fill dirt are not the same product
They are priced very differently and confusing them is a mistake you notice a season later.
- Fill dirt is subsoil. No organic matter, nothing living in it. It is for changing the grade of the ground, building up a low spot, or backfilling. Nothing grows well in it.
- Topsoil is screened surface soil. It is the base layer for a new lawn or a new bed, and it varies enormously in quality between suppliers — ask what is in it.
- Garden soil or raised bed mix is topsoil already blended with compost, sold ready to plant into. It costs the most and it is what you want in the top layer of a bed.
- Compost on its own is a soil amendment, not a growing medium. Filling a bed entirely with compost gives you something that holds too much water and slumps as it breaks down.
For a raised bed, a blend is the usual answer: roughly half topsoil, a third compost, the rest something for drainage. Many suppliers sell that pre-mixed by the yard.
Soil settles, so expect to top up
Fresh soil is full of air. A raised bed filled level to your target depth in spring will be visibly lower by autumn — commonly an inch or two in the first season, more if the mix is compost-heavy.
That is not a reason to overfill. Soil heaped above the rim washes out. It is a reason to plan on a top-up bag or two next season, and to add compost annually as a matter of routine rather than treating the first fill as final.
Bulk yards are measured loose in the truck, so a delivered yard also settles once it is spread and watered. Between that and the settling above, the honest expectation is that you will be within about a bag either way of the number here, and that a raised bed will want more soil next year regardless.
Weight, if you are collecting it
Screened topsoil runs around 2,200 lb per cubic yard when dry and noticeably more after rain. A half-ton pickup’s payload is typically 1,500 to 2,000 lb, so one cubic yard per trip is the practical maximum — and a yard of wet soil is already over that.
This is an estimate. Volume arithmetic is exact for the dimensions you entered; the uncertainty is in settling and in how loose the delivered material is. Buy to the number here and expect to want a little more, not less.