How much topsoil do I need?
For a new lawn, New Mexico State University's turfgrass guide says the absolute minimum soil depth is 4 inches, and to add topsoil until there is 4 – 6 inches after firming. For deep roots it recommends 6 inches or more. The depths are after firming, so loose soil from a truck or a bag will settle: allow a little extra.
Source New Mexico State University Extension · Guide H-509, Turfgrass Establishment ↗
How to calculate topsoil
Here it is with your numbers:
- Find the area: 20 × 10 = 200 sq ft.
- Change the depth to feet: 4 ÷ 12 = 0.3333 ft.
- Multiply the area by the depth: 200 × 0.3333 = 66.6667 cu ft.
- Round to two decimal places: 66.67 cu ft.
- Divide by 27 for cubic yards: 66.6667 ÷ 27 = 2.4691 cu yd.
- Round to two decimal places: 2.47 cu yd.
- Divide by the bag size: 66.67 ÷ 0.75 = 88.8933, rounded up to 89 bags.
It means you need 2.47 cubic yards of topsoil. In bags, buy 89 bags of 0.75 cu ft: bags are rounded up so you don't run short.
For a round bed, measure all the way across and pick Circle. For an odd shape, split it into rectangles, or type its square footage.
Source Common Core State Standards · Grade 6, volume V = l × w × h (6.G.A.2) ↗Common Core State Standards · Grade 7, area of a circle (7.G.B.4) ↗NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
How far one cubic yard of topsoil goes
One cubic yard is 27 cubic feet, so it covers 81 square feet at 4 inches.
Topsoil bags in a cubic yard
Bags are sold by volume, for example Scotts Premium Topsoil comes in 0.75 cubic foot bags. Bags needed for one cubic yard, rounded up:
| Bag size | Bags per cubic yard |
|---|---|
| 0.75 cu ft | 36 |
| 1 cu ft | 27 |
| 1.5 cu ft | 18 |
Source ScottsMiracle-Gro · Scotts Premium Topsoil (bag size) ↗
FAQs
How much topsoil do I need?
Multiply the area in square feet by the depth in feet (inches ÷ 12), then divide by 27 for cubic yards. For a lawn, New Mexico State University's guide gives 4 inches as the minimum and 4 – 6 inches after firming. A 20 ft × 10 ft patch at 4 inches needs 2.47 cubic yards.
Source New Mexico State University Extension · Guide H-509, Turfgrass Establishment ↗
How many bags of topsoil are in a yard?
A cubic yard is 27 cubic feet, so divide 27 by the bag size: 36 bags of 0.75 cubic feet, 27 bags of 1 cubic foot or 18 bags of 1.5 cubic feet.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
Sources
- New Mexico State University Extension: Guide H-509, Turfgrass Establishment
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement
- Common Core State Standards: Grade 6, volume V = l × w × h (6.G.A.2)
- Common Core State Standards: Grade 7, area of a circle (7.G.B.4)
- ScottsMiracle-Gro: Scotts Premium Topsoil (bag size)