R
Real Gravel.
Washed Aggregate & Pipe Displacement Model

French Drain Gravel Calculator

Calculate clean washed drainage rock for trenches in cubic yards and tons.

Interactive Dimension BlueprintDepth: 18"
Length: 20 ft10 ft
Drainage Rock (1.5" - 2.5" Washed)•Includes 3D compacted volume estimate

1Project Shape & Dimensions

ft
ft

2Gravel Type & Density

Large, clean open-graded stone that leaves large void spaces for high-velocity water movement. Does not clog with silt.

Best for:French DrainsCulvert OutletsRetaining Wall BackfillSeptic Drain Fields

3Gravel Depth & Compaction

Typical for Drainage: 6"
inches depth
Recommended: 10%

Accounts for roller compaction settlement, uneven ground contours, and wheelbarrow spill.

Material & Delivery Cost Estimator

Ordering Checklist
  • Bulk delivery dump trucks usually require a 10–12 ft wide clearance path.
  • Always verify if your quarry quotes in Tons or Cubic Yards.
  • Order ~10% extra to prevent having to pay a second delivery fee for a half-ton deficit.

French Drain Trench Sizing & Gravel Guide

Trench LengthDimensions (W × D)Gravel Volume (yd³)Washed Stone (Tons)Pipe Displacement
25 Feet 12" W × 18" D 1.31 yd³ ~1.77 US Tons -2.18 cu ft (4" pipe)
50 Feet 12" W × 18" D 2.62 yd³ ~3.54 US Tons -4.36 cu ft (4" pipe)
100 Feet 12" W × 18" D 5.23 yd³ ~7.06 US Tons -8.73 cu ft (4" pipe)

French Drain FAQs

Q: What is the best gravel for a French drain?

The best gravel for a French drain is washed, clean 3/4" to 1.5" crushed stone (#57 or drainage rock). Never use crushed stone with dust or fine particles (like crusher run), as the dust will wash down and permanently clog the drainage pipe perforations.

Q: How do you calculate gravel for a French drain trench?

Calculate total trench volume: Trench Length (ft) × [Width (inches) ÷ 12] × [Depth (inches) ÷ 12] = Total Trench Cubic Feet. Next, subtract the volume displaced by the 4-inch perforated pipe (approx 0.087 cu ft per linear foot). Divide remaining cubic feet by 27 to find cubic yards, then multiply by 1.35 tons/yd³.

Q: How much gravel do I need for a 50-foot French drain?

For a standard 50-foot long trench that is 12 inches wide and 18 inches deep: Total trench volume is 75 cu ft. Subtracting pipe displacement (4.35 cu ft) leaves 70.65 cu ft of aggregate needed = 2.62 cubic yards (~3.54 US tons of washed drainage stone).