The gravel calculation formula
All gravel calculations start with the same three-step formula:
- Find your volume: Cubic yards = (length ft × width ft × depth in) ÷ 324
- Add a waste allowance: Cubic yards ordered = volume × 1.10 (for a 10% buffer)
- Convert to tons: Tons = cubic yards × material density (1.30–1.40 ton/yd³)
The divisor 324 is the canonical landscaping shortcut: 27 cu ft per cubic yard × 12 in per foot = 324. It lets you enter depth in inches (the intuitive way) without manually dividing by 12 first.
For example: a 20 × 10 ft garden bed at 3 in deep = (20 × 10 × 3) ÷ 324 = 1.85 cu yd. At 1.35 ton/yd³ (pea gravel) with 10% waste: 1.85 × 1.10 = 2.04 cu yd × 1.35 ≈ 2.75 tons.
Recommended depths by project type
| Project | Depth | Waste |
|---|---|---|
| Decorative accent / mulch substitute | 1–2 in | 5–10% |
| Garden path or stepping stones | 2–3 in | 10% |
| Patio, fire-pit surround | 2–4 in | 10% |
| Driveway surface (gravel) | 3–4 in | 15% |
| Driveway base (crusher run) | 4–6 in | 15–20% |
| Paver sub-base | 4–6 in | 15% |
| French drain / drainage channel | 6–12 in | 10% |
Why add a waste allowance?
No gravel installation is perfectly efficient. Stone gets kicked out of bounds, spreads uneven, spills off a truck or wheelbarrow, and — for compacted bases — the material physically compresses to a lesser depth. The 10% default covers normal spreading waste and slight over-fill at edges. For compacted bases (crusher run, paver base), use 15% because compaction removes 15–25% of loose volume.
Tons vs cubic yards: what your supplier needs
Suppliers weigh bulk gravel at the scale house and sell by the ton. Once you know your cubic yards, multiply by the material density to get tons:
- Pea gravel (3/8"): 1.35 ton/yd³
- Crushed stone #57 (3/4"): 1.40 ton/yd³
- River rock (1–3"): 1.30 ton/yd³
- Paver base / crushed concrete: 1.40 ton/yd³
- Crusher run / dense-grade: 1.40 ton/yd³
Always confirm the density with your local supplier — wet or freshly crushed stone can weigh 10–15% more than dry lab values.
Use the calculator
Enter your dimensions below for an instant result.