Gravel base calculator
A compacted base is what keeps a slab from settling. This sizes the aggregate you need including a compaction allowance, because loose material loses volume when you run a plate compactor over it.
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This calculator needs JavaScript. The reference table below covers the common cases.
| Base depth | yd³ per 100 ft² | Approx. tons |
|---|---|---|
| 3 in | 1.11 | 1.5 |
| 4 in | 1.48 | 2.0 |
| 6 in | 2.22 | 3.0 |
| 8 in | 2.96 | 4.0 |
The formula
length × width × (depth ÷ 12) ÷ 27 × (1 + compaction allowance) = cubic yards
Worked example
20 × 24 ft at 4 in with 20% compaction: 160 ft³ ÷ 27 × 1.2 = 7.1 yd³, roughly 9.6 tons.
Reference table
| Base depth | yd³ per 100 ft² | Approx. tons |
|---|---|---|
| 3 in | 1.11 | 1.5 |
| 4 in | 1.48 | 2.0 |
| 6 in | 2.22 | 3.0 |
| 8 in | 2.96 | 4.0 |
Assumptions
- Weight assumes roughly 2,700 lb per cubic yard for crushed stone; actual density varies by material.
- Compaction allowance of 20% is typical for crushed aggregate.
- Base thickness and material type should follow the slab design and local practice.