Gravel Calculator for French Drain
Estimate trench volume, pipe displacement, clean stone order quantity, fabric wrap width, cubic yards, tons, and bag counts for French drain layouts.
French Drain Material Estimate
| Preset | Typical Use | Width x Depth | Pipe OD | Default Stone |
|---|---|---|---|---|
| Yard Walkway | Small surface water run | 8 in x 18 in | 4.25 in | 3/4 in clean |
| Foundation Edge | House perimeter drainage | 12 in x 24 in | 4.25 in | No. 57 stone |
| Driveway Interceptor | Catch runoff before pavement | 12 in x 30 in | 4.25 in | 1 in clean |
| Retaining Wall | Back-of-wall drain zone | 12 in x 24 in | 4.25 in | No. 57 stone |
| Dry Well Lead | Pipe run into stone pit | 18 in x 36 in | 4.25 in | 2 in clean |
| Gravel Type | Typical Bulk Density | Drainage Suitability | Void Behavior |
|---|---|---|---|
| 3/4 in clean crushed stone | 2,700 lb/yd3 | Excellent | Stable, angular gaps |
| No. 57 washed stone | 2,650 lb/yd3 | Excellent | Consistent drainage voids |
| Washed pea gravel | 2,800 lb/yd3 | Moderate | Rounded, shifts more easily |
| 1 in clean angular stone | 2,600 lb/yd3 | Excellent | Larger open structure |
| River rock | 2,850 lb/yd3 | Moderate | Rounded and less interlocked |
| Trench Section | Wrap Formula | Common Roll Check | Field Note |
|---|---|---|---|
| Narrow yard drain | 2 x depth + width + overlap | 36 to 48 in rolls | Keep seam above stone |
| Foundation drain | 2 x depth + width + overlap | 48 to 60 in rolls | Trim only after backfill starts |
| Deep curtain drain | 2 x depth + width + overlap | 60 to 72 in rolls | Wide fabric avoids seam tension |
| Wide dry well lead | 2 x depth + width + overlap | 72 in or split wrap | Overlap fabric, never leave gaps |
| Output | Formula Used | Rounding | Best Use |
|---|---|---|---|
| Cubic yards | Net ft3 / 27 | Round up by order | Bulk delivery or pickup |
| Tons | yd3 x lb/yd3 / 2000 | Round to load size | Quarry and landscape yards |
| Volume bags | Order ft3 / bag ft3 | Whole bags | Small drains and repairs |
| Weight bags | Total lb / bag lb | Whole bags | When bags list weight only |
Every time it rains, your basement stinks of wet earth. Annoying, yes, but it’s also a signal: Water wants more of your yard than you do and that’s never a good thing. The usual solution is to dig a hole, toss some gravel in there, and solve the problem. But nope… Most of the time, that doesn’t work, since removing soil isn’t realy the issue; it’s physics.
You need a system to carry water away from your house. This calculator do the math for you after you input your trench measurements. That way, you’ll know if you has enough rock to make a difference.
How to Build a Good French Drain
Most French drains fail for one simple reason: They use wrong kind of gravel. The stone you choose makes all the difference. You want something clean and angular (think No. Use 57 or three-quarter-inch crushed rock. The individual pieces has sharp edges that lock together to create stable gaps that allow water to move through.
River rock or round pea gravel may be prettier then that in the garden, but it will shift around readily, packing down over time as its void space is reduced. Turning your drain to a solid column of stone that doesn’t move water; rather, it holds it back. Sounds counterintuitive, right? I know it’s just ugly, jagged rocks, but this is when function beats form every single time. Single. Time.
Homeowners typically make mistakes in sizing the trench because they believe bigger is always better, though it isn’t. Just making something deep doesn’t ensure good performance. You want plenty of volume so there is room for the pipe itself, a cushion of gravel surrounding it, and more gravel to allow for settling. You’ll need enough volume to accommodate the pipe and a generous layer of stone around it (and don’t forget that the tool factors out amount displaced by the pipe; it simply occupies space that wouldn’t be gravel-filled, so failing to account for this will result in either insufficient material ordered, or a trench too shallow to handle high volumes of water).
For residential purposes, a standard four-inch perforated pipe should suffice as long as you have a minimum of a one-percent slope. This means gravity will do most of the work. Even a small incline will help guide water nicely toward the discharge point.
The surprising part that determines the long-term success of this system is fabric. Without it, the gravel will over time has its voids filled with migrating soil fines, which will in turn plug up the drain in a matter of years. The fabric is your sieve, allowing water to pass through but blocking the dirt. The calculator help estimate the amount of geotextile required by measuring the width and depth of the trench and accounting for overlap needed at the seams.
The seam overlap isn’t optional; any gap in your wrap will be found immediately by the soil, which will take full advantage of it. But a dozen inches of overlap insures continuity and no bypasses where sediment-laden water could simply make its way right past the drainage area. You’ll need to order enough, which takes some forethought because stone will settle as you backfill the trench. This waste factor ensures that you don’t have to make multiple trips back to the yard for more.
For bigger jobs, it’s typically less expensive to have bulk delivered. For smaller fixes, like using bags, you get more precise ordering. The converters are also nice if you’re not sure exactly what to do with your pile, letting you convert cubic yards to bags or tonnage and vice versa. Better to come away with too much rather than running out mid-line.
In the end though, installing a French drain is an investment in both peace of mind and dryness. Using the right materials and techniques takes careful preparation. However, knowing what matters, like how wide to wrap the fabric or how sharp the stones should be… Makes it feel much less intimidating. When done well, the drainage system protects your house and lets you use your yard instead of becoming a hidden problem.
So do yourself a favor and start with clean stone and accurate measurements. You’ll thank me for it the next time you try to take a shortcut.
