Drainage & Structural · Contractor Estimation Tool

French Drain Gravel Calculator

Calculate washed #57 drainage stone and pea gravel needed for French drain trenches, curtain drains, and weeping tiles.

Found this free aggregate calculator helpful for your project?

Support our free contractor tools & engineering guides with a coffee!

How the French Drain Gravel Calculator Works

Washed angular stone (such as ASTM #57, 3/4" clean stone) with minimal fines for high load-bearing capacity and free water drainage. Our French Drain Gravel Calculator computes exact geometric volume in cubic feet and cubic yards, then converts volume into US short tons (2,000 lbs) using the typical bulk density of Crushed Stone (#57 Clean Angular Stone) (2,700 lb/yd³ or 1.35 tons/yd³).

Mathematical Formula for French Drain Gravel:
1. Area (sq ft) = Length (ft) × Width (ft)
2. Volume (cu ft) = Area (sq ft) × [Depth (inches) ÷ 12]
3. Volume (cu yd) = Volume (cu ft) ÷ 27
4. Recommended Volume = Base Volume × (1 + 10% Ordering Adjustment)
5. Estimated Tons = Recommended Cubic Yards × 1.35 tons/yd³

Step-by-Step Worked Example

Example Project: 50 ft × 1.5 ft Area at 18 Inches Depth (+10% Adjustment)

Surface Area: 50 ft × 1.5 ft = 75 sq ft.
Base Volume: 75 sq ft × (18 ÷ 12) = 112.5 cu ft (4.17 cubic yards).
With +10% Ordering Adjustment: 4.17 yd³ × 1.10 = 4.58 cubic yards.
Weight in US Short Tons: 4.58 yd³ × 1.35 tons/yd³ = 6.19 tons (12,375 lbs).

Primary Applications & Contractor Best Practices

Concrete slab and shed sub-bases: Engineered for reliable coverage, drainage stability, and long-term performance.
Retaining wall backfill and drainage zones: Engineered for reliable coverage, drainage stability, and long-term performance.
Driveway intermediate layer (over coarse base): Engineered for reliable coverage, drainage stability, and long-term performance.
French drains and dry wells: Engineered for reliable coverage, drainage stability, and long-term performance.

Coverage & Tonnage Quick Reference Table (Crushed Stone (#57 Clean Angular Stone))

Estimated cubic yards and US short tons (including +10% ordering adjustment) across common project square footages:

Project Area	2" Depth	3" Depth	4" Depth	6" Depth
100 sq ft	0.92 t (0.68 yd³)	1.38 t (1.02 yd³)	1.83 t (1.36 yd³)	2.75 t (2.04 yd³)
250 sq ft	2.29 t (1.70 yd³)	3.44 t (2.55 yd³)	4.58 t (3.40 yd³)	6.88 t (5.09 yd³)
500 sq ft	4.58 t (3.40 yd³)	6.88 t (5.09 yd³)	9.17 t (6.79 yd³)	13.75 t (10.19 yd³)
1,000 sq ft	9.17 t (6.79 yd³)	13.75 t (10.19 yd³)	18.33 t (13.58 yd³)	27.50 t (20.37 yd³)
1,500 sq ft	13.75 t (10.19 yd³)	20.63 t (15.28 yd³)	27.50 t (20.37 yd³)	41.25 t (30.56 yd³)

Frequently Asked Questions

Multiply your project length (50 ft) by width (1.5 ft) to get area (75 sq ft). Multiply by depth in feet (18 in ÷ 12 = 1.50 ft) to get 112.5 cubic feet, then divide by 27 to get 4.17 base cubic yards. Adding a 10% ordering adjustment gives 4.58 yd³, which equals 6.19 US short tons at 2700 lb/yd³.

One cubic yard (27 cubic feet) of Crushed Stone (#57 Clean Angular Stone) weighs approximately 2,700 pounds, or 1.35 US short tons (100 lbs per cubic foot). Typical regional quarry densities range between 2,550 and 2,850 lb/yd³.

For most french drain gravel installations, a typical compacted depth is 4 inches (our default preset uses 18 inches). Always excavate soft organic topsoil and install woven or non-woven geotextile fabric before spreading aggregate.

At 1.35 tons per cubic yard, 1 US short ton equals 0.74 cubic yards (20.0 cu ft). That covers approximately 120 sq ft at 2" deep, 80 sq ft at 3" deep, and 60 sq ft at 4" deep.