Drainage Rock Calculator 2026 - Estimate Tons & Cost for Drainage

For a standard French drain trench measuring 1 foot wide and 1 foot deep, you need approximately 0.037 cubic yards or 0.05 tons of drainage rock per linear foot. A 50-foot trench requires about 1.85 cubic yards or 2.5 tons. Always add 10% for waste and voids.

For deeper trenches at 18 inches deep and 12 inches wide, you need about 0.056 cubic yards per linear foot. That same 50-foot trench would require 2.78 cubic yards or approximately 3.75 tons of 3/4" clean drainage rock. Use our French drain gravel calculator for custom dimensions.

Drainage rock is clean crushed stone without fines, allowing water to flow freely through the voids. Base rock contains fine particles (minus) that compact into a solid, stable surface. Never use base rock for drainage, as the fines will block water flow and cause flooding.

Using the wrong material is a critical construction error. Base rock is designed to lock together and support heavy loads, making it perfect under concrete or pavers. Drainage rock is designed to remain porous. For structural support, use the crushed stone calculator to estimate base materials.

3/4-inch to 1.5-inch clean crushed stone is the best size for French drains. Angular edges lock together to prevent shifting while maintaining 25-35% void space for water flow. Avoid pea gravel because its smooth shape causes it to shift and restrict water movement.

For heavy drainage applications like large dry wells or commercial retention areas, 1.5-inch clean stone provides even larger void spaces for high water volume. For septic drain fields, local codes typically mandate clean stone between 3/4 and 1.5 inches. Decorative river rock should never be used for functional drainage. Calculate decorative stone needs with our river rock calculator.

In 2026, drainage rock costs $45 to $85 per ton or $60 to $110 per cubic yard. Delivery fees range from $50 to $150. For large projects over 10 tons, bulk quarry pricing often drops to $35 to $55 per ton.

Home improvement stores charge significantly more at $5 to $8 per 0.5 cubic foot bag (over $200 per ton). For any project requiring more than half a cubic yard, order bulk delivery from a local quarry to save 50% or more. Estimate your total project expenses using our excavation cost calculator.

A retaining wall drainage column should be 12 to 18 inches wide and extend from the base footing to within 6 inches of the top of the wall. You need enough drainage rock to fill this entire vertical column behind the wall to prevent hydrostatic pressure buildup.

Hydrostatic pressure is the leading cause of retaining wall failures. The drainage column must be wrapped in non-woven geotextile fabric and have a perforated drain pipe at the base to carry the water away. Always backfill with clean drainage rock, not native soil.

Yes, always wrap drainage rock in non-woven geotextile fabric. The fabric prevents soil from clogging the voids between the rocks, which maintains water flow. Without fabric, silt and clay will fill the gaps within 1 to 3 years, causing the drain to fail.

Use non-woven filter fabric, not woven landscape fabric. Non-woven fabric allows water to pass through while blocking fine soil particles. Overlap fabric seams by at least 6 inches and wrap the rock completely, closing the top seam with landscape staples or zip ties.

One ton of drainage rock typically equals 0.74 to 0.8 cubic yards, depending on the stone size and density. Standard 3/4-inch clean stone weighs about 1.35 tons per cubic yard, meaning 1 cubic yard weighs approximately 2,700 pounds.

To convert your project volume to tons, multiply cubic yards by 1.35. For example, 5 cubic yards x 1.35 = 6.75 tons. Clean drainage rock is lighter per yard than base rock because the lack of fines creates more air voids between the stones.

No, do not use pea gravel for drainage. Pea gravel is smooth and round, causing it to shift under pressure and compact tightly, which blocks water flow. Angular clean crushed stone is required because it interlocks for stability while leaving void spaces for water to pass through.

Pea gravel also migrates over time due to its smooth shape, creating uneven surfaces. For decorative above-ground applications like garden beds or walkways, pea gravel works well. But for any subsurface drainage, foundation backfill, or French drain, always use angular clean crushed stone. For landscape applications, reference the landscape rock calculator.