How to use this calculator
- Measure trench length. Total linear feet of the drain run. For complex layouts, sum each segment.
- Set width and depth. Standard: 12" wide × 18–24" deep. For commercial or footing drains: 24" wide × 36" deep.
- Subtract pipe volume. A 4-inch perforated pipe displaces about 0.087 ft³ per linear foot of trench — small but worth subtracting on long runs.
- Read your tons + yards. Order #57 stone (clean, angular, drains well) or 3/4" clean gravel — never crusher run for french drains.
Formula
Volume (yd³) = Trench Length × Width × Depth ÷ 27 (less pipe volume)
Worked example
A 50 ft french drain at 12" wide × 18" deep: 50 × 1 × 1.5 = 75 ft³ ÷ 27 = 2.78 yd³ of stone. Subtract pipe volume (~0.16 yd³) and you need about 2.6 yd³ or 3.6 tons of #57 stone.
Common project sizes
Quick reference for the most common french drain gravel calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| 30 ft × 12" × 18" | 45 ft³ | ~1.5 yd³ · ~2 tons |
| 50 ft × 12" × 18" | 75 ft³ | ~2.6 yd³ · ~3.6 tons |
| 100 ft × 12" × 24" | 200 ft³ | ~7 yd³ · ~10 tons |
| Foundation drain (120 ft × 24" × 36") | 720 ft³ | ~25 yd³ · ~35 tons |
2026 cost reference
Typical retail price range in the United States for french drain gravel. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per ton (#57 stone delivered)
$30 – $70
Clean 3/4" angular stone is $20–$35/ton at the quarry, $30–$70/ton delivered. Add ~$1.50/lin ft for 4-inch perforated pipe and ~$0.30/lin ft for fabric.
Tips for accurate results
- Use #57 stone (3/4" angular) or 3/4" clean — these drain freely. Crusher run plugs solid with fines and defeats the drain.
- Always wrap the trench in landscape fabric (geotextile) to prevent soil migration into the gravel. Without it, drains clog in 3–5 years.
- Slope the trench at least 1% (1 in per 100 ft) toward daylight or a dry well. Without slope, water pools.
- Fill the bottom 2 in with gravel before laying the perforated pipe (holes facing down). Add 4 in of stone over the pipe; finish with topsoil and turf.
- Order 10% extra to account for trench wall settling and bedding.
When to consult a pro
French drains are a workable DIY project for short runs (under 50 ft) with hand digging. For longer runs, foundation drains, or any drain that interfaces with municipal storm sewer, hire a pro — improper pitch or undersized pipe makes drains useless and the diagnosis (water still pooling, basement still wet) is expensive to retrace.