Rock
Drain Rock Calculator
Calculate the drain rock needed for French drains, foundation drainage, and dry wells.
Inputs
3/4-inch drain rock is the standard for French drains and foundation drainage — angular washed stone that locks together.
Live estimate
Material needed
18.52 cu yd
- Cubic yards
- 18.52 cu yd
- Tons
- 25.93 tons
- Truckloads
- 1.54
- Area
- 500 sq ft
- Cubic feet
- 500
You will likely need
- •18.52 cu yd — material needed
- •Schedule 2 truck loads
- •Approximate delivered weight: 25.93 tons
Supplier tip
Most suppliers sell drain rock by either the cubic yard or by weight. Confirm your supplier's preferred ordering unit before purchasing.
Weight estimates are based on industry-standard average material densities. Actual delivered weights may vary by supplier and moisture content.
Diagram
Live estimate
- Mathematical quantity
- 19 cu yd
- Drain rock void ratio is a drainage property, not an order allowance
- Informational
- Field conditions
- Not applied
- Adjusted requirement
- 19 cu yd
- Ordering rule
- Round up to whole ton
- Suggested order
- 19 cu yd
Clean drain rock is engineered to have voids for flow. That is a functional property; it does not translate to a blanket volume allowance on top of trench geometry.
What you actually need in the field, before rounding to a supplier-friendly ordering unit.
Estimator confidence
HighCrushed and rounded rock has void space between particles, but bulk-yard cubic yards already reflect that packing. No automatic order allowance is added; consider a user-selectable edge-migration condition where borders are open.
Improve confidence: Depth should be at least 2× the largest stone dimension; edge migration on open borders is a separate consideration.
Why this behavior applies: The geometric cubic-yard requirement is what the yard sells. Void space is a physical property, not evidence to add a percentage.
- Trench cross-section — Trench width and depth drive volume more than surface length.
- Whether pipe is bedded and surrounded — Full-envelope beds need noticeably more rock than pipe-under-only.
- Confirm rock size — ¾ to 1½ inch angular washed stone is the standard for French drains.
- Slope the pipe at least 1% and confirm the outlet before backfilling.
- Compact backfill in lifts if the trench crosses a driveway or walk.
- Using pea gravel instead of angular washed stone — pea gravel clogs.
- Skipping filter fabric and burying the fines that later plug the drain.
- Under-ordering rock, then compacting a partial trench that no longer drains.
Smart tips
- Ordering 5–10% extra is standard on irregular layouts. Running short costs more than the excess.
- You're just over one truckload — a slightly larger truck could save a delivery fee.
- Enter your dimensions to see live material estimates.
How it's calculated
Area is derived from your shape inputs and converted to sq ft.
Depth is converted to feet; cubic feet = area × depth.
Cubic yards = cubic feet ÷ 27, then × (1 + waste %) × (1 + compaction %).
Estimated tons = cubic yards (with waste) × 1.4.
Truckloads = cubic yards (with waste) ÷ truck capacity.
Total cost = cubic yards (with waste) × price per cubic yard + delivery.
Professional guidance
When to use drain rock
French drains, foundation footing drains, dry wells, and subgrade drainage for retaining walls.
Recommended depth
12+ inches of stone in French drains, wrapped in filter fabric. 6 inches minimum under retaining walls.
Pro tip
Always wrap drain rock in non-woven filter fabric to prevent silt from clogging the voids.
Common mistakes
Using pea gravel — the small size clogs. Use ¾–1½ inch angular washed rock.
Material assumptions
- Drain rock density: about 1.4 tons per cubic yard.
- Typical sizes: ¾–1½ inch angular washed stone.
- French drains: 12 inches of stone around perforated pipe.
Frequently asked questions
Related calculators
Related articles
Deeper guidance from the Learn library — sizing, depth, waste, and ordering for this material.
- River Rock Size GuideRiver rock comes in sizes from pea-sized to fist-sized. Each has a specific use. Here's the full breakdown.
- How Deep Should Decorative Rock Be?Two inches for ground cover, three for weed suppression, four to six for driveways. Depth is a durability decision, not just an aesthetic one.
- French Drain Gravel Calculator GuideA French drain is only as good as its rock. Here's how to size the trench, pick the right stone, and calculate the exact volume you'll need.
These results are estimates only. Confirm quantities, compaction, waste, and delivery requirements with your supplier or project professional before ordering materials.