Bulk material is sold by the cubic yard, and one cubic yard covers 324 square feet at one inch deep. Everything else is arithmetic from there.
The calculation
Cubic yards = (length in feet × width in feet × depth in inches) ÷ 324
A bed 20 feet by 10 feet at 3 inches deep: (20 × 10 × 3) ÷ 324 = 1.85 cubic yards. Order 2.
For irregular beds, break the area into rectangles and circles, calculate each, and add them together. Rounding up slightly is normal — running short mid-job costs more than the extra material.
Depth by use
| Material | Typical depth | Notes |
|---|---|---|
| Mulch, established beds | 2–3 in | Deeper suppresses weeds no better and holds excess moisture |
| Mulch, refresh over existing | 1–2 in | Measure what is already there first |
| Topsoil, over existing lawn | 0.25–0.5 in | Thicker smothers the grass |
| Topsoil, new bed or lawn | 4–6 in | Depends on what is underneath |
| Gravel, walkway | 2–3 in | Over a prepared base |
| Gravel, driveway | 4–6 in | In layers, compacted |
Common mistakes
- Mulch volcanoes. Mulch piled against tree trunks traps moisture against the bark and invites rot and pests. Pull it back from the trunk.
- Mulch against siding. Same problem, applied to your house.
- Burying the existing layer. Old mulch that has not broken down should be loosened or removed before adding more. Otherwise depth accumulates until it holds water in the root zone.
- Gravel without a base. Gravel spread over unprepared soil migrates into the soil and disappears. The base is what keeps it where you put it.
- Topsoil over compacted ground. Adding soil on top of compacted subsoil does not fix drainage. It creates a shallow layer that holds water.
Ordering
Measure first, calculate second, and confirm delivery access — trucks need room to maneuver and a place to dump. Where the pile lands determines how far every wheelbarrow load has to travel.