How deep to go
| Use | Published figure | Source |
|---|---|---|
| Compacted crushed stone | 4 to 6 in | premierpools.com |
| Pad size beyond the spa | 6 to 12 in on every side | premierpools.com |
| Crushed stone minimum (Site Prep) | 4 in | siteprep.com |
Premier Pools & Spas tells owners to mark an area 6 to 12 inches larger than the spa on all sides, add crushed stone in 2- to 3-inch layers and compact each one, for 4 to 6 inches total. Site Prep says a properly built pad has at least 4 inches of crushed stone and a border to hold it, and that an 8 × 8 ft pad on level ground takes about 1 ton. Check your spa maker's warranty terms before you build.
Working it out
Cubic yards = area (sq ft) × depth (in) ÷ 12 ÷ 27. Tons = cubic yards × weight per cubic yard.
Example: 9 × 9 ft at 4 inches with 10% extra is 1.10 cubic yards of no. 57 stone, about 1.42 tons at 1.29 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 hot tub pad?
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://premierpools.com/blogs/hot-tub-info-customer-guides/spa-site-preparation
- https://www.siteprep.com/gravel-bases-for-hot-tubs/
- https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/15034/003.cfm