Gravel Calculator for French Drains
French drains channel standing yard water away from your foundation. A standard trench is 12" to 18" deep and 8" to 12" wide, lined with non-woven geotextile fabric, a 4" perforated pipe, and backfilled with #57 clean washed round stone.
Instant Gravel & Stone Estimator
Calculate exact US tons, cubic yards, and 50lb bag counts with compaction allowance.
77.7 cu ft (+10% compaction)
~54 bags per cubic yard
Disclaimer: Calculations provided are estimates for preliminary material planning only. Actual yields vary based on subgrade compaction, site grading, waste, and local trade practices. QuickRenoTools assumes no liability for material shortages, structural failures, code non-compliance, vehicle overloads, or jobsite injuries. Verify all structural spans, retaining wall heights, and concrete mix designs with a licensed engineer, certified contractor, or local building authority prior to purchase and construction. Legal Disclaimer→
Gravel Calculator for French Drains — Quick Reference
Exact material counts across standard depths and load ratings.
| Trench Length (12×18") | Gravel Volume (Cu Yds) | Bulk Weight (Tons) | 50 lb Retail Bags | Delivery & Drainage Notes |
|---|---|---|---|---|
| 25 ft Trench (12"W × 18"D) | 1.39 cu yds | N/A (Bulk: 1.8 Tons) | 70 bags (50lb) | Subtract ~0.1 cu yd for 4" pipe displacement. |
| 50 ft Trench (12"W × 18"D) | 2.78 cu yds | N/A (Bulk: 3.6 Tons) | 140 bags (50lb) | Order bulk delivery from local landscape quarry. |
| 100 ft Trench (12"W × 18"D) | 5.56 cu yds | N/A (Bulk: 7.2 Tons) | 280 bags (50lb) | Full tandem dump truck load. |
Disclaimer: Calculations provided are estimates for preliminary material planning only. Actual yields vary based on subgrade compaction, site grading, waste, and local trade practices. QuickRenoTools assumes no liability for material shortages, structural failures, code non-compliance, vehicle overloads, or jobsite injuries. Verify all structural spans, retaining wall heights, and concrete mix designs with a licensed engineer, certified contractor, or local building authority prior to purchase and construction.
Related Tools for This Project
Building this project? Don't forget your sub-base gravel, reinforcement steel, or finishing supplies:
Step 1: Outlets — Pouring a concrete catch basin or discharge headwall for pipe daylighting.
Step 2: Surface Restoration — Re-sodding or patching grass turf over your backfilled trench.
Step 3: Runoff Protection — Channeling water away from an existing or planned paver patio.
Project Guide: Gravel Calculator for French Drains
When building a project of this scale, precision in your prep work directly impacts durability. Ensure you excavate below the topsoil layer down to undisturbed subsoil, and always install compacted aggregate base with edge forms braced at minimum 2-foot intervals.
Frequently Asked Questions: Gravel Calculator for French Drains
Common questions about bag calculations, ordering bulk vs bags, and trade standards.
What size gravel is best for a French drain?
Use 3/4-inch washed clean crushed stone (commonly known as #57 stone) or smooth 3/4-inch river gravel. Never use crushed run, crusher run, or stone dust, as fine particles will immediately clog the filter fabric and pipe.
Do I need to wrap the gravel or the pipe in fabric?
Always wrap the entire gravel envelope (burrito method) using 4 oz non-woven landscape filter fabric. This allows water to enter from the sides and top while preventing subsoil and silt from infiltrating the gravel void spaces.
Should perforated pipe holes face up or down in a French drain?
Always face the holes DOWN. As groundwater rises from below the trench, it enters the holes from the bottom and flows away down the pipe before the water level ever reaches your lawn surface.
What slope is required for a French drain to work properly?
Maintain a minimum slope of 1% (a 1-inch drop for every 8 to 10 feet of horizontal run). This ensures gravity rapidly moves water to your discharge outlet or pop-up emitter.
Which pipe is best: corrugated perforated pipe or smooth PVC?
Solid-wall perforated PVC (Schedule 40 or thin-wall SDR 35) is far superior to black corrugated flex pipe. Smooth interior walls move water 40% faster, resist root crushing, and can be easily cleaned with a sewer snake.
How deep and wide should a residential French drain trench be?
A standard trench is 12 inches wide and 18 to 24 inches deep. This allows for 2 inches of gravel under the pipe, the 4-inch pipe, and 10 to 14 inches of washed stone backfill.
Can you cover a French drain with sod and grass?
Yes. Wrap the top of the fabric over the gravel, add 3 to 4 inches of coarse sandy topsoil, and lay grass sod. For maximum surface drainage in problem flood zones, leave the top gravel exposed to create an open French drain.
How long does a properly installed French drain last?
When built with non-woven geotextile fabric, washed #57 stone, and smooth PVC pipe, a French drain lasts 30 to 50+ years with virtually zero maintenance.
Where should a French drain discharge its water?
Discharge into a municipal storm drain (where permitted), an open hillside ditch, a dry well, or daylight the pipe onto a downward lawn slope with an automatic spring-loaded pop-up emitter.
How much gravel do I need per 10 feet of French drain trench?
For a 12" wide by 18" deep trench, you need approximately 0.55 cubic yards (0.75 tons) of #57 washed gravel for every 10 linear feet of trench.