How deep to go
| Use | Published figure | Source |
|---|---|---|
| Pea gravel, 9 in | protects to a 5 ft fall | ndsu.edu |
| Sand, 9 in | protects to a 4 ft fall | ndsu.edu |
| Wood mulch, 9 in | protects to a 7 ft fall | ndsu.edu |
| Wood chips, 9 in | protects to a 10 ft fall | ndsu.edu |
| Recommended install depth | 12 in | ndsu.edu |
The table above is CPSC's minimum compressed loose-fill depths as printed by NDSU Extension. CPSC recommends at least 12 inches of loose fill under and around public play equipment, because the material compresses by about a quarter. For equipment taller than 5 ft, pea gravel at 9 inches is not enough; wood mulch or chips protect to greater heights.
Working it out
Cubic yards = area (sq ft) × depth (in) ÷ 12 ÷ 27. Tons = cubic yards × weight per cubic yard.
Example: 20 × 20 ft at 12 inches is 14.8 cubic yards of pea gravel, about 19.3 tons at 1.30 tons per cubic yard.
Rochester Concrete Products' install guide adds 10% for compaction and uneven ground.
Common questions
How much gravel do I need for a playground surfacing?
Measure the area, choose a depth from the table above and enter both in the calculator. It gives cubic yards, tons and bags.
Should I order extra?
Rochester Concrete Products' install guide adds 10% for compaction and uneven ground. Loose stone also compacts, so a compacted layer needs more loose material than its finished depth suggests.
Related calculators
Sources
- https://www.ndsu.edu/agriculture/sites/default/files/2023-01/fn1374.pdf
- https://www.cpsc.gov/s3fs-public/pdfs/blk_media_325.pdf
- https://hellogravel.com/guides/2025-gravel-prices-per-ton-delivered-cost-calculator-and-regional-rates/
- https://www.thecalculatorsite.com/articles/units/how-much-cubic-yard-weigh.php