How Much Gravel for a 100 Foot French Drain?
A typical French drain trench is about a foot wide and 18 inches deep. Over 100 feet, minus the space the 4-inch pipe takes up, that is 5.23 yards of stone. How much gravel for a 100 foot French drain by weight: about 7.3 tons.
Volume and tonnage calculator →Gravel by trench size over 100 feet
| Trench (W × D) | Cubic yards | Tons |
|---|---|---|
| 6 × 12 in | 1.53 | 2.1 |
| 12 × 18 in | 5.23 | 7.3 |
| 12 × 24 in | 7.08 | 9.9 |
| 18 × 24 in | 10.79 | 15.1 |
Figures subtract a 4-inch pipe and assume about 1.4 tons per yard of washed stone.
Related: How Much Gravel for a 10 Foot French Drain?
Which gravel
Washed angular stone around 3/4 inch is the usual pick. Avoid crusher run or anything with dust; the point is open space for water to move. See the best gravel for a French drain.
Wrap and slope
Give the drain a steady fall of about 1 inch per 8 to 10 feet, around 11.1 inches over 100 feet, and make sure it outlets somewhere the water can go. Wrap the stone in filter fabric so soil does not migrate in. Call 811 before digging.
Related: How Much Gravel for a 20 Foot French Drain?
Measuring the run
Lay out the route with paint, measure its length and note the start and end elevations. A line level or a laser level confirms you have enough fall. Plan the trench width around your shovel or trencher size.
Common mistakes
Many French drains fail because silt clogs the stone, often from missing or torn fabric. Others have dips in the pipe that trap water. Keep the slope steady and the stone clean.
Cost and tools
Gravel is the bulk of the material cost, followed by pipe and fabric. Renting a trencher saves a lot of digging on long runs. A wheelbarrow, a flat shovel and a level finish the toolkit.
Questions people ask
How many tons of gravel for a 100 ft French drain?
About 7.3 tons for a 12x18 inch trench.
How many yards of gravel for a 100 ft French drain?
About 5.23 cubic yards.
What size gravel for a French drain?
Clean washed stone around 3/4 inch, such as #57.
How much slope does a French drain need?
About 1 inch of fall per 8 to 10 feet.
Do I need fabric for a French drain?
Yes, non-woven filter fabric keeps soil out of the stone.
Related guides
- Best Gravel for a French Drain: Size and Type
- French Drain Along an Asphalt Driveway
- How Much Gravel for a 60 Foot French Drain?
- How Much Gravel for a 75 Foot French Drain?
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