Drainage Rock Calculator
Estimate the drainage rock you need for French drains, dry wells and yard drainage.
1. Measure length and width in the same unit. For circles, measure the diameter across the widest point.
2. Pick a depth: 2 in for decorative beds, 3 in for walkways, 4–6 in for driveways.
3. Add waste and compaction: 5–10% waste for spillage. 15–20% compaction if you'll drive on it.
4. Pick the right material: crushed stone compacts well for base layers; pea gravel is best for decorative surfaces.
Based on Crushed stone (#57) at 1.5 tons/yd³.
A 20 ft × 10 ft area at 3 in depth ≈ 1.85 yd³ ≈ 2.5 tons of material.
How the Drainage Rock Calculator helps you plan
The Drainage Rock Calculator takes the guesswork out of drainage rock. Instead of hand-converting units or guessing at coverage, you enter simple measurements and receive quantities you can hand directly to a supplier.
It is tuned for typical residential landscaping — beds, borders, paths, and small backyard projects — but the underlying math scales to commercial jobs when you enter larger dimensions.
- Coverage estimates in square feet and square meters
- Depth-based volume so you never over- or under-buy
- Bagged and bulk equivalents side-by-side
- Optional pricing to see the full project cost
Choosing the right depth
Depth is the single biggest driver of cost. For mulch and decorative drainage rock, 2–3 inches is usually enough to smother weeds and retain moisture. For paths and driveways you'll want 4–6 inches over a compacted base.
If you're topping up an existing area, only count the new depth you're adding — not the total. A quick re-measurement each spring will save a full delivery over the life of the bed.
When to order in bulk vs. bags
Bags are convenient for jobs under about a cubic yard. Above that, bulk delivery is cheaper per unit and easier to spread. The Drainage Rock Calculator shows both totals so you can compare at a glance.
If access is tight (narrow gates, upstairs terraces), bags may still win despite the higher unit cost, simply because a bulk load has nowhere to go.