How topsoil is calculated
Soil is sold by the cubic yard when it comes on a truck and by the cubic foot when it comes in bags. The calculator finds the volume of the area at the depth you want, adds any settling allowance, and reports the result in yards, bags and tons.
area (ft²) = length × width or π × (diameter ÷ 2)²
volume (ft³) = area × depth in inches ÷ 12
cubic yards = volume ÷ 27
yards to order = cubic yards × (1 + settling % ÷ 100)
bags = yards to order × 27 ÷ bag size in ft³, rounded up
tons = yards to order × pounds per yard ÷ 2,000
Weights are typical for loose, moist material from the material weight per cubic yard chart: about 2,000 lb for topsoil, 2,100 lb for fill dirt and 1,100 lb for compost.
Worked example: 20 × 10 ft area, 4 in deep
The calculator opens on a 20 × 10 ft area covered 4 in deep with topsoil, priced in 0.75 ft³ bags.
- Area: 20 × 10 = 200 ft².
- Volume: 200 × 4 ÷ 12 = 66.7 ft³.
- Cubic yards: 66.7 ÷ 27 = 2.47 yd³. Bulk soil sells by the half or whole yard, so order 2.5 yd³.
- Bags: 66.7 ÷ 0.75 = 88.9, rounded up to 89 bags.
- Weight: 2.47 × 2,000 ÷ 2,000 = 2.47 tons.
Add a 10% settling allowance and the same area needs 2.72 yd³, and the order becomes 3 yd³.
How deep to spread soil
The right depth depends on the job. About 2 in is enough to top-dress an existing lawn and level shallow dips. A new lawn wants 4–6 in of topsoil over the subsoil, and garden beds 8–12 in. A raised bed is filled to its full depth: an 8 × 4 ft bed that is 12 in deep holds 32 ft³, which is 1.19 yd³ or 32 one-cubic-foot bags of compost.
Fill dirt and compost use the same volume math but do different jobs. Fill dirt is subsoil with clay and rock in it: good for raising grade and backfilling, poor for growing. Compost is a soil amendment, usually worked into the top few inches of a bed rather than spread as a layer on its own, and at about 1,100 lb a yard it is much lighter to move.
- Measure depth from the finished grade you want down to the existing surface, at several points, and use the average.
- Split an irregular yard into rectangles and circles and enter each one with “+ Add another area”. Each area can have its own depth, so a lawn top-dressing and a deep garden bed go in the same order.
- If you are filling a low spot with fill dirt and capping it with topsoil, run the calculator twice: once for each layer.
Settling, weight and hauling
Loose soil settles about 10% once it is watered, rolled and walked on. If you are building up to a set grade, such as against a patio edge or a new foundation, enter that as the settling allowance so the finished surface ends up where you want it. For a top-dressing that will be raked in, you can leave it at 0.
Soil is heavy, and payload runs out long before the bed is full. These are rules of thumb from the material weight chart; the sticker in the driver's door jamb gives your truck's real payload.
| Vehicle | Payload, lb | yd³ per load | Topsoil, lb |
|---|---|---|---|
| Half-ton pickup (F-150, Silverado 1500 class) | 1,500 | 0.5 | 1,000 |
| Three-quarter-ton pickup (2500 class) | 2,500 | 1 | 2,000 |
| One-ton pickup (3500 class) | 3,500 | 1.5 | 3,000 |
| Dump trailer, 10 ft (10,000 lb GVWR class) | 7,000 | 2.5 | 5,000 |
For the default example, 2.47 tons is 4,938 lb, or about 5 trips in a half-ton pickup against one delivery. Above a couple of yards, delivery is usually the simpler choice.
Sources
- Geometry: rectangle area = length × width; circle area = π × (diameter ÷ 2)²; 1 yd³ = 27 ft³
- Material weight per cubic yard chart (typical loose, moist bulk densities from supplier data; truck rules of thumb)
- Settling allowance for loose topsoil: about 10% (common supplier and landscaper guidance)
- Retail soil bag sizes: 0.75 ft³ (40 lb), 1 ft³ and 1.5 ft³