French Drain Gravel Calculator
Estimate cubic feet, cubic yards & tons of drainage stone — includes pipe volume subtraction and a 10% waste buffer
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1
Enter Trench Dimensions
Add the trench length, width, and gravel depth. Width and depth default to inches — the most common way to measure a trench.
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2
Add Pipe Diameter (Optional)
If your French drain includes a perforated pipe, enter its diameter in inches. The pipe volume will be subtracted for a closer gravel estimate.
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3
Select Drainage Stone Type
Choose the drainage stone you plan to use. This affects the ton estimate — confirm the exact density with your supplier.
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4
Click Calculate
Results appear here — trench volume, gravel volume in cubic feet and yards, estimated tons, and optional cost.
French Drain Gravel Calculator for Yards and Tons
Ordering gravel for a drainage trench can be harder than it looks. A few extra inches of depth or a longer trench can change your order by a full cubic yard. Use this French Drain Gravel Calculator to turn your measurements into a clear estimate before contacting a gravel supplier.
Enter the trench length, width, and depth. Then choose the drainage stone type and include the pipe diameter if needed. The calculator gives you a useful starting estimate — your local supplier can confirm the exact material weight.
- Trench Volume in Cubic Feet
- Cubic Yards for Bulk Orders
- Pipe Volume Subtraction
- Tons by Material Type
- 10% Waste Buffer
- Optional Cost Estimate
What Does a French Drain Gravel Calculator Measure?
The calculator measures the empty trench space that will be filled with drainage stone
Trench Volume
Length × Width × DepthThe full inside trench space. Measure the inside of the trench, not the wider excavation area, for an accurate starting volume.
Pipe Displacement
Pipe Volume SubtractedIf a perforated pipe runs through the trench, its cylindrical volume is subtracted from the trench total. This matters more on longer trenches.
Waste Allowance
10% Buffer IncludedTrench walls are rarely perfect and some gravel is lost during spreading. A 10% buffer prevents running short before the installation is complete.
The result is shown in three units: cubic feet for checking the calculation, cubic yards for bulk gravel orders, and tons when your supplier sells gravel by weight.
How to Calculate Gravel for a French Drain
Measure the trench in feet — convert all inch measurements before using the formula
Step-by-Step Calculation Method
- Measure the trench length from the water collection area to the outlet.
- Measure the inside trench width and the planned gravel depth.
- Convert inches to feet. For example, 12 inches equals 1 foot, 18 inches equals 1.5 feet.
- Multiply length × width × depth to find cubic feet.
- Subtract the pipe space if your installation includes a perforated pipe. Enter the pipe diameter to have this done automatically.
- Divide by 27 to convert cubic feet into cubic yards.
- Add a 5% to 10% waste allowance for normal trench variation, spreading, and uneven ground.
- Convert cubic yards into tons using your supplier's material density factor.
French Drain Gravel Formula
Three formulas turn trench measurements into a gravel order estimate
Use the full trench volume for a quick planning number. For a more accurate estimate, subtract the pipe volume before adding a small waste allowance.
A trench is 50 ft long, 12 inches wide, and 18 inches deep, with a 4-inch perforated pipe.
At 1.4 tons/yd³, this project needs approximately 4 tons of drainage gravel. Confirm the exact density with your supplier before ordering.
What Gravel Should You Use for a French Drain?
Use clean drainage stone that leaves open spaces for water to move through the trench
Your local supplier may call it #57 stone, washed crushed stone, drainage rock, or clean angular gravel. Ask the supplier which material is best for drainage in your area and request the exact tons-per-yard weight before placing the final order.
| Gravel Type | Best Use | Planning Note |
|---|---|---|
| #57 stone or clean crushed stone | Most residential French drains | A common choice because water can flow through open spaces |
| Washed angular stone | Pipe bedding and trench backfill | Often used where stable drainage fill is needed |
| Pea gravel | Only where a local drainage design allows it | Check with an installer or supplier before using it |
| Crushed drainage rock | Long drainage trenches and larger projects | Available sizes and weights vary by supplier |
#57 Stone / Clean Crushed Stone
The go-to choice for residential French drains. Uniform stone size leaves plenty of open space for water movement and doesn't clog as easily as fines-heavy material.
Washed Angular Stone
Angular edges interlock to create a stable, firm fill around the pipe. Often used for pipe bedding where the trench needs additional structural support.
Pea Gravel
Smooth and round — may shift or not provide the same drainage performance. Only use where a local drainage design specifically allows it. Ask your installer first.
How Much Gravel Should You Order?
Start with the calculator total, then use these checks before placing the order
Measure Inside the Trench
- Measure the inside trench dimensions, not the wider excavation area.
- Keep all measurements in the same unit before converting.
- A wider measurement increases the estimate significantly.
Include Pipe Displacement
- Enter the pipe's outside diameter for a closer gravel estimate.
- Pipe displacement is small for short drains but matters on longer runs.
- A 4-inch pipe in a 50-foot trench displaces about 4.4 cubic feet.
Confirm Supplier Density
- Ask for the supplier's material density or tons-per-yard factor.
- Gravel density changes by stone type, size, and moisture content.
- Many suppliers sell by whole yards, half yards, or full tons.
Add a Waste Buffer
- Add a 5% to 10% buffer for normal trench variation and spreading loss.
- Round up to the supplier's available delivery unit.
- Check whether the delivery truck can safely access your site.
French Drain Planning Notes Before You Dig
Gravel quantity is only one part of a working French drain — plan the full drainage route before excavation
The trench also needs a safe outlet and a consistent fall toward that outlet. A perforated pipe, clean drainage stone, and suitable filter fabric can help reduce soil movement into the gravel.
Water should move away from the problem area and discharge in a safe, permitted location. Avoid directing water toward neighboring properties, foundations, walkways, or areas that may cause erosion.
Ready to Estimate Your French Drain Gravel?
Enter your trench dimensions, choose your drainage stone, and add the pipe diameter for a more accurate estimate. Confirm tons-per-yard and delivery details with your local supplier.
Start Calculating NowFrequently Asked Questions
Common questions about calculating gravel for French drain projects
Multiply trench length × width × gravel depth to get cubic feet. Subtract pipe volume when needed, divide by 27 for cubic yards, then add a small waste allowance. The calculator above handles all these steps automatically.
Measure the inside of the trench, not the full yard area. Enter the length, width, and depth into the French drain gravel calculator above, then round up to your supplier's order unit.
Calculate each trench separately, then add the cubic-yard totals together. Include each branch's individual width and depth because they may not all be the same size.
It should — and this calculator does. Pipe displacement may be small for short drains, but it matters more on longer trenches or when you want a tighter gravel estimate. Enter the pipe diameter in the Perforated Pipe field to subtract it automatically.
A 5% to 10% buffer is a sensible allowance for normal trench variation, spreading, and uneven ground. The calculator includes a 10% buffer automatically. Use a larger buffer only when the site is irregular or the supplier has a minimum order size.
Yes. Enter the full trench dimensions and leave the Pipe Diameter field empty. The calculator will estimate the gravel needed to fill a gravel-only drainage trench without subtracting any pipe volume.
Gravel density can change based on stone type, size, moisture, and local material. The calculator uses common planning densities. Always use your supplier's stated tons-per-yard factor for the final order.
Other Gravel Calculators
Need estimates for other project types? Try one of these
Crushed Gravel Calculator
Driveways & BasesNeed gravel for a compacted base or driveway project? The Crushed Gravel Calculator estimates yards, tons, and cost for crusher run, 3/4 stone, and granite.
Use CalculatorPea Gravel Calculator
Landscaping & PathsFor decorative landscape stone, patios, walkways, and playgrounds. The Pea Gravel Calculator shows cubic yards, tons, bags, and cost.
Use CalculatorDriveway Gravel Calculator
DrivewaysEstimate gravel for any driveway size and depth. Supports multiple gravel types, shape options, and an optional cost estimate.
Use CalculatorPlan Your French Drain Gravel Order With Confidence
Measure the inside of your trench, use the calculator to estimate cubic yards and tons, and allow a small buffer so the project does not stop short. Confirm utility locations and local drainage requirements before excavation.