Topsoil depth by job
4–6 inches settled for a new lawn, 6–8 inches for borders, 12–16 inches for root vegetables and ¼ inch or less per top-dressing.
| Job | Depth | Source |
|---|---|---|
| New lawn | at least 4–6 in, firmed or settled | Penn State[1] |
| New lawn (UK) | 100–150 mm | Rolawn[2] |
| Borders and general planting | 150–200 mm | Rolawn[2] |
| Shallow-rooted vegetables | 150–200 mm | Rolawn[2] |
| Root vegetables | 300–400 mm | Rolawn[2] |
| Raised bed on a hard surface: greens, beans, cucumbers | at least 8 in | Univ. of Maryland[3] |
| Raised bed on a hard surface: tomatoes, peppers, squash | 12–24 in | Univ. of Maryland[3] |
| Top-dressing a lawn with compost | ¼ in or less per application | Cornell[5] |
New lawns: 4 to 6 inches, settled
Penn State Extension recommends a minimum of 4–6 inches of good-quality topsoil for a new lawn, and specifies that as the firmed or settled depth.[1] Loose soil straight from the truck will sink, so spread a little more than the target. The same guide suggests mixing about 2 inches of the new topsoil into the upper 2–3 inches of subsoil and tilling at least 4 inches deep.[1] Then seed it: the grass seed calculator converts your lawn area into pounds of seed.
Beds and vegetables
A UK topsoil producer recommends 150–200 mm for borders and shallow-rooted crops, and 300–400 mm for root vegetables.[2] For raised beds built on paving, University of Maryland Extension sets minimum soil depths by crop and suggests a compost and topsoil mix of about 1:2 or 1:1.[3]
Compost instead of (or with) topsoil
Colorado State gives compost rates for improving existing soil rather than adding a new layer:[4]
- Lawn, one time: 1–2 inches worked into the top 6 inches.
- New vegetable or flower beds: 3–4 inches worked into the top 8–12 inches.
- Existing beds each year: about ¼ inch.
They also give the rule of thumb behind every number on this site: three cubic yards cover about 1,000 square feet at 1 inch deep.[4]
Top-dressing a lawn
Cornell's sports turf guidance limits compost top-dressing to about ¼ inch per application, and uses 1/8 to 3/8 inch for light seeding layers.[5] Small depths still add up over a large lawn:
| Depth | Cubic yards | Cubic feet |
|---|---|---|
| 1/8 in | 0.39 | 10 |
| ¼ in | 0.77 | 21 |
| 3/8 in | 1.16 | 31 |
| ½ in | 1.54 | 42 |
| ¾ in | 2.31 | 63 |
Cornell's own table rounds these to 0.4, 0.8, 1.2, 1.5 and 2.3 cubic yards.[5]
Cubic yards per 1,000 square feet
Each inch of topsoil takes about 3.1 cubic yards per 1,000 sq ft: 12.3 yards at 4 inches and 18.5 at 6 inches.
| Depth | Cubic yards | 1 cu ft bags | m³ per 100 m² |
|---|---|---|---|
| 2 in | 6.2 | 167 | 5.08 |
| 4 in | 12.3 | 334 | 10.16 |
| 6 in | 18.5 | 500 | 15.24 |
| 8 in | 24.7 | 667 | 20.32 |
| 12 in | 37 | 1,000 | 30.48 |
Bagged garden soil is sold in sizes from 0.75 to 2 cu ft,[6] which is practical for beds but not for a whole lawn. Use the topsoil calculator for your own area, or the raised bed soil calculator for beds.
Don't compact what you just spreadSoil structure matters as much as depth. USDA NRCS figures show root growth being restricted once dry bulk density passes roughly 1.47–1.8 g/cm³, depending on soil texture.[7] Keeping heavy traffic off newly spread soil helps it stay below those levels.
Frequently asked questions
How much topsoil do I need for a new lawn?
At least 4–6 inches, settled.[1] That is 12.3–18.5 cubic yards per 1,000 sq ft.
Is 2 inches of topsoil enough for grass?
How deep should topsoil be for a vegetable garden?
150–200 mm (6–8 in) for shallow-rooted crops and 300–400 mm (12–16 in) for root vegetables.[2]
How much compost should I add to a garden bed?
For a new bed, 3–4 inches worked into the top 8–12 inches; for existing beds, about ¼ inch a year.[4]
Sources
- Lawn Establishment
- Calculating topsoil requirements
- Soil to Fill Raised Beds
- Choosing a Soil Amendment (Fact Sheet 7.235)
- Topdressing (Sports Field Management)
- Miracle-Gro Garden Soil All Purpose (product label)
- Bulk Density is an Indicator of Soil Health (reproducing the USDA NRCS Soil Health Educators Guide)