GravelCalculator.us offers a free online French drain gravel calculator that estimates drain rock, perforated pipe, and filter fabric for a French drain, which is a gravel-filled trench that carries water away through a pipe. It is designed for US homeowners, landscapers, and contractors who need reliable takeoff quantities for one straight trench.The tool returns the rock in cubic yards and short tons with the pipe volume subtracted, plus pipe length and geotextile fabric area. It is an estimate only: it does not design drainage, check slope, or choose an outlet, so enter your trench measurements below and confirm the stone and final quantity with your supplier before you order.

Calculate Your Trench Gravel

Enter one straight trench to get order quantities. For a trench with bends or a changing depth, calculate each straight section separately and add the results together.

• Trench length: Measure the run in feet from inlet to discharge point.
• Trench width: Enter width in inches (standard is 12 inches; heavy-flow runs use 18 inches).
• Trench depth: Enter total excavation depth in inches (typically 18 to 24 inches).
• Pipe type and size: Select nominal size (4-inch pipe with 4.5-inch outside diameter is the residential standard).
• Stone density: Planning density for clean washed stone (#57 stone is approximately 1.40 tons per cubic yard).
• Waste allowance: 10% industry standard allowance accounts for trench sidewall irregularities and settling.
• Price per ton or cubic yard: Optional input for instantaneous material cost takeoffs.

Who This Calculator Is For

This calculator is for anyone ordering drain rock for one straight French drain trench:

• Homeowners who have water pooling in a low spot, across a patio edge, or near a home foundation
• Landscapers who quote multiple drainage installations each season and need rapid bills of materials
• Contractors who order bulk aggregates from local quarries that bill by weight in short tons

This calculator is not for:

• Civil hydraulic drainage design or stormwater engineering
• Utility trench structural backfill calculations
• Whole-project turnkey installation costing (labor, machinery, disposal fees)
• Surface swales or non-trench drainage types

What You Get

The calculator returns exact quantities for one trench run:

How to Get Your Estimate

Measure the trench, enter the numbers into the calculator, and order the quantities returned:

1. Measure the straight run: Determine the total linear distance from the start of the trench to the gravity outlet point.
2. Enter dimensions: Provide trench length in feet, along with width and depth in inches.
3. Select pipe size: Choose your perforated pipe. The calculator automatically subtracts the pipe’s physical outside displacement volume.
4. Verify stone density: Confirm the density with your local gravel quarry (default is 1.40 tons/yd³ for washed #57 stone).
5. Set waste factor: Use 10% for standard clean digs, or up to 15% for rocky, uneven soil.
6. Read order summary: Take the net cubic yards, tons, pipe sticks, and fabric rolls directly to your materials supplier.

Formulas

Every calculation uses these standard civil engineering volumetric formulas. For a straight trench run, pipe length matches trench length:

Worked Example: 50 Feet with a 4-Inch Pipe

Consider a typical residential yard trench: 50 feet long, 12 inches wide, and 18 inches deep, with a standard 4-inch nominal Schedule 40 or corrugated pipe (4.5-inch true outside diameter):

• Gross trench volume: 50 ft × 1.0 ft × 1.5 ft = 75.0 cu ft (2.78 cubic yards)
• Pipe displacement: π × (0.1875 ft)² × 50 ft = 5.52 cu ft (0.20 cubic yards)
• Topsoil cap: 3 inches of topsoil = 50 ft × 1.0 ft × 0.25 ft = 12.5 cu ft (0.46 cubic yards)
• Net gravel volume: 75.0 − 5.52 − 12.5 = 56.98 cu ft × 1.10 (10% waste) = 62.68 cu ft = 2.32 cubic yards
• Stone weight (#57 stone at 1.40 tons/yd³): 2.32 yd³ × 1.40 tons/yd³ = 3.25 short tons
• Filter fabric envelope: (1 ft + 2 × 1.25 ft + 1 ft overlap) × 50 ft × 1.05 = 236 sq ft (1 standard 3′ × 100′ roll)
• Perforated pipe: 50 linear feet = five 10-foot sticks

Notice: The pipe displaces roughly 7% to 8% of the trench void. Failing to subtract the pipe displacement leads to over-ordering rock by almost a quarter-yard.

How These Numbers Were Checked

You can check the rock volume, weight, pipe length, and fabric area by hand using the formulas above.

• Stone density: Bulk density changes with stone gradation, void ratio, and moisture content. This tool uses dry, loose bulk planning density (1.40 tons/yd³ for washed crushed #57 stone). The quarry delivery scale ticket establishes your legally certified billed weight.
• Pipe displacement: Rather than using nominal interior diameters (ID), this calculator computes water displacement using true outside diameters (OD)—4.5 inches for 4″ pipe and 6.625 inches for 6″ pipe—for mathematical accuracy.

Gravel Cost for Your Order

Enter your supplier’s price per ton or per cubic yard in the optional cost estimator to project materials expenditures. For project-wide hardscaping and driveway subgrade estimates, compare costs using our primary Gravel Calculator or Crushed Stone Calculator.Always request a delivered quote in writing from your local quarry. Inquire whether delivery is flat-rate or per loaded mile, whether a minimum tonnage fee applies, and how local sales taxes are levied on freight.

Before You Dig and Order

Complete these critical site preparation steps before picking up a shovel or ordering materials:

• Call 811: State and federal laws require calling 811 (Call Before You Dig) at least 2 to 3 business days before breaking ground. Public utility locators mark underground power, gas, communications, and water lines at zero cost to you.
• Hand-dig within utility buffers: When excavating within 24 inches of marked utility lines, use hand tools only—never an excavator or trencher.
• Set a minimum slope: A gravity French drain requires a continuous downward fall of at least 1% (1/8 inch drop per foot) or preferably 2% (1/4 inch per foot) toward the discharge outlet.
• Plan the discharge outlet: Water must discharge safely away from neighboring properties. Options include daylighting onto a downward slope, a dedicated dry well, or a pop-up emitter. If discharge flow could cause ground erosion, armor the outfall with rock from our Rip Rap Calculator.
• Check permit rules: Connecting a yard drain to municipal stormwater gutters, curb outlets, or street culverts frequently requires local public works permits.
• Excavation safety: Trenches deeper than 4 feet can present cave-in hazards. Follow OSHA trench safety practices and keep spoils back at least 2 feet from trench rims.

Frequently Asked Questions

Will a French drain fix my water problem?

A French drain is ideal for surface runoff and high groundwater pooling in yard low spots or saturating foundation perimeters. However, if water infiltrates through basement walls due to hydrostatic floor pressure, interior perimeter weeping tile may be required. Have a drainage professional inspect severe foundation issues.

How accurate are the results?

The geometric math is exact. Total tonnage accuracy depends on the density of the aggregate supplied. Always confirm the stone’s dry loose density with your quarry dispatcher and add 10% waste for irregular earthen sidewalls.

Which stone should I buy for a French drain?

Order clean, washed, angular #57 crushed granite, limestone, or washed river rock (around 3/4-inch to 1-inch diameter). Never use crusher run, road base, or unwashed gravel with stone dust, as fine silt will clog the filter fabric and perforations within months.

How deep and wide should the trench be?

Standard residential yard drains are 10 to 12 inches wide and 18 to 24 inches deep. Heavy-volume perimeter drains intercepting deep groundwater may require a 16-to-18-inch width and 24-to-36-inch depth.

What if my trench bends?

Calculate each straight trench segment separately, then add the resulting material volumes. Remember to purchase 45-degree or 90-degree elbows, tees, or cleanout wyes for every bend in your piping run.

Do I need a permit?

Interior backyard drainage rarely requires a building permit, but discharging water toward public streets, wetlands, or stormwater sewers often requires city approval. Always check with your local municipal engineering department.

Your Order Checklist

1. Confirm stone is clean, washed #57 crushed rock (no fines or quarry dust).
2. Check the quarry’s billed density (standard is 1.40 tons per cubic yard).
3. Confirm truck delivery access, clearance height, and dump location.
4. Order non-woven needle-punched geotextile fabric (avoid woven landscape weed barrier).
5. Call 811 and verify all utility markings before breaking ground.

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