Drainage Gravel Calculator
Estimate how much clean drainage stone you need for a French drain, footing drain, or drainage bed, based on trench size and depth.
Measure straight across the widest point.
Adjust depth below if needed.
Covers spillage and compaction. 5–10% is normal.
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Bags or bulk delivery?
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Coverage & weight
Material profile
For a 30 ft French drain trench, 1 ft wide, with 3 inches of stone, you’ll need about 0.31 cubic yards, or roughly 0.38 tons of clean 3/4 inch drainage stone including 10% waste. Wrap the stone in filter fabric to keep it from clogging with soil.
Drainage stone needed for common project sizes
These estimates use clean 3/4 inch drainage stone at 2,500 lb per cubic yard with a 10% waste allowance built in.
| Project | Depth | Cubic yards | Tons |
|---|---|---|---|
| Short French drain, 20 sq ft | 3 in | 0.20 yd³ | 0.25 tons |
| Long French drain, 100 sq ft | 3 in | 1.02 yd³ | 1.27 tons |
| Footing drain perimeter, 210 sq ft | 4 in | 2.85 yd³ | 3.57 tons |
| Downspout drainage bed, 36 sq ft | 3 in | 0.37 yd³ | 0.46 tons |
| Culvert bedding, 60 sq ft | 6 in | 1.22 yd³ | 1.50 tons |
| Drainage dry well, 16 sq ft | 24 in | 1.30 yd³ | 1.63 tons |
Drainage stone types, density and drainage rating
| Type | Weight per yd³ | Best for | Drainage |
|---|---|---|---|
| Clean 3/4″ drainage stone | 2,500 lb | French drains, drain fields | Excellent |
| Clean 1.5″ drainage stone | 2,450 lb | Perimeter drains, culverts | Excellent |
| Pea gravel (drainage grade) | 2,700 lb | Shallow drainage beds | Good |
Figures are for dry material. Wet or freshly delivered material can weigh noticeably more.
How to calculate drainage gravel you need
- Measure the trench or bed length × width for a drain field or bed, or trench length × width for a French drain.
- Set the depth 3in of stone below and around the pipe for a French drain, 4in for a footing drain.
- Convert to cubic yards multiply the area by depth in feet and divide by 27.
- Add 10% waste covers backfill loss and irregular trench walls.
- Convert to tons multiply cubic yards by clean stone density (2,450-2,700 lb/yd³) and divide by 2,000 — clean stone is lighter than graded gravel since it has no fines filling the voids.
Worked example
Using the calculator’s default 30 ft × 1 ft French drain trench with 3 inches of clean 3/4 inch stone:
- Trench area30 ft × 1 ft = 30 sq ft
- Depth in feet3 in ÷ 12 = 0.25 ft
- Volume30 sq ft × 0.25 ft = 7.5 cu ft
- Raw cubic yards7.5 ÷ 27 = 0.28 yd³
- Plus 10% waste0.28 × 1.10 = 0.31 yd³
- Weight (clean 3/4 in stone, 2,500 lb/yd³)0.31 × 2,500 ÷ 2,000 = 0.38 tons
- Order amountAbout 0.4 tons — roughly 15 bags at 50 lb each, often more practical than a bulk minimum for short runs
Recommended depth by project
| Project | Recommended depth | Notes |
|---|---|---|
| Project type | Depth | Notes |
| French drain around pipe | 3 in | Stone surrounds the pipe on the sides and above, plus a base layer below |
| Footing / foundation drain | 4 in | Wrap in filter fabric to keep soil from clogging the voids |
| Drainage bed / dry well | 3-4 in per layer | Build in lifts for large pits; line the pit walls with fabric |
| Downspout splash bed | 3 in | Shallow bed spreads roof runoff away from the foundation |
| Culvert bedding | 6 in | Deeper bed cushions and beds the culvert pipe |
Bags or bulk delivery?
Bagged clean stone (typically 50 lb bags) costs more per ton than bulk delivery, but for short French drain runs the total volume is often small enough that bags are still the practical choice — you avoid paying a delivery fee for a fraction of a ton. Once a job needs a full pallet or more, bulk delivery is cheaper.
- Small jobsunder 0.5 ton, short French drain runs under about 30 ft — bagged stone avoids paying a delivery fee for a small volume.
- Medium jobs0.5 to 2 tons, footing drains around a small structure — compare bag total to bulk plus delivery.
- Large jobsover 2 tons, full perimeter footing drains or drain fields — bulk delivery only; bags become impractical to carry and cut open.
Common mistakes
- Using gravel with fines instead of clean stonegraded gravel packs with dust and sand that clog drainage voids; only washed, open-graded stone drains properly.
- Skipping filter fabricwithout fabric wrapping the stone, surrounding soil migrates into the voids over a few seasons and the drain stops working.
- Not sloping the trenchFrench drains need consistent fall — about 1% minimum — toward the outlet; a flat or reverse-graded trench lets water pool instead of flowing out.
- Undersizing the outleta well-built drain still backs up if the daylight outlet or dry well it empties into is too small or gets blocked.
- Confusing drainage stone with base courseclean, no-fines stone has poor load-bearing capacity and should not be used under a driveway or slab.
- Placing perforated pipe the wrong wayperforated pipe orientation matters — holes generally face down for edge drains to collect water at the pipe invert, so check the design before backfilling.
What this calculator assumes
Adjust your result if your project differs from these.
- Depth includes only the stone layer surrounding the pipe, not the total trench excavation depth.
- Density reflects clean, washed, angular stone with no fines, lighter than graded gravel because there are no fines filling the voids.
- 10% waste covers backfill loss and irregular trench walls.
- Filter fabric, pipe, and outlet fittings are not included in this material estimate.
- Prices are material only; excavation, fabric, and pipe are separate.
- Bag coverage assumes standard 50 lb bags.
Common questions
What size stone is best for a French drain?
3/4 inch clean stone is the standard choice — it drains well, resists clogging, and is small enough to handle easily around pipe.
Do I need filter fabric around drainage gravel?
Yes — wrap the stone (and pipe) in filter fabric to keep surrounding soil from migrating into the voids and clogging the drain over time.
How deep should a French drain trench be?
Total trench depth is typically 18-24 inches, but the stone layer itself is usually just 3 inches below the pipe plus enough above to cover it — that stone depth is what this calculator sizes.
Can I use pea gravel for a French drain?
Pea gravel works for shallow drainage beds and downspout runoff, but 3/4 inch clean stone drains better and resists clogging around perforated pipe.
How much does drainage gravel weigh per cubic yard?
About 2,450 to 2,700 lb (1.2 to 1.35 tons) — clean stone is lighter than graded gravel because it has no fines filling the voids between stones.
What's the difference between drainage gravel and regular gravel?
Drainage or “clean” stone is washed and screened to remove sand and dust, leaving open voids for water to flow through. Regular graded gravel has fines that pack tight and drain poorly.
How long can a French drain run be?
Most residential runs work well up to about 100 feet per outlet; longer runs need a larger pipe diameter or a second outlet to keep water moving.
Do I need perforated pipe with drainage gravel?
Not always — a gravel-only “French drain” works for short, shallow runs, but adding perforated pipe increases capacity for larger volumes of water.
How much drainage gravel do I need for a downspout bed?
A 36 sq ft bed at 3 inches deep needs about 0.37 cubic yards, or roughly 0.46 tons including waste.
Can drainage gravel be used as a driveway base?
No — clean, no-fines stone has poor load-bearing capacity. Use graded aggregate base course for driveways and roads instead.
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Project
| Shape | — |
| Dimensions | — |
| Depth | — |
| Area | — |
| Material | — |
| Waste allowance | — |
Volume & weight (incl. waste)
| Cubic yards | — |
| Cubic feet | — |
| Weight | — |
| Tons (rounded up) | — |
Shopping list
| Bulk order | — |
| Bagged alternative (0.5 cu ft) | — |
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes uniform depth and standard dry material densities. Confirm quantities with your supplier before ordering.