Free French Drain Gravel Calculator for Trench Volume, Pipe Displacement, Cubic Yards, and Stone Weight
Use this browser-side calculator to turn measurements and material assumptions into a practical first-pass estimate. Review the formulas, verify units, and confirm product, code, or site details before purchasing or building.
Use the calculator
How to use this calculator
1. Measure consistently
Use the units shown beside each input and recheck measurements before relying on the estimate.
2. Set real assumptions
Replace default coverage, waste, density, spacing, or yield with actual project or product data when available.
3. Verify before ordering
Treat the output as a planning number, then compare it with drawings, packaging, supplier data, codes, and site conditions.
12 useful features
Trench length
Built into this calculator for a clearer planning workflow.
Trench width
Built into this calculator for a clearer planning workflow.
Fill depth
Built into this calculator for a clearer planning workflow.
Pipe diameter
Built into this calculator for a clearer planning workflow.
Gross volume
Built into this calculator for a clearer planning workflow.
Pipe displacement
Built into this calculator for a clearer planning workflow.
Net gravel volume
Built into this calculator for a clearer planning workflow.
Waste allowance
Built into this calculator for a clearer planning workflow.
Cubic-yard conversion
Built into this calculator for a clearer planning workflow.
Optional tonnage
Built into this calculator for a clearer planning workflow.
Local history
Built into this calculator for a clearer planning workflow.
Copy/download/print/reset
Built into this calculator for a clearer planning workflow.
Formula and reference table
| Concept | Formula / meaning | Planning note |
|---|---|---|
| Gross trench | length × width × depth | All dimensions converted to feet |
| Pipe displacement | π × radius² × length | Cylinder volume |
| Net gravel | trench volume − pipe volume | Cannot fall below zero |
| Stone weight | cubic yards × density | Density is user-adjustable |
Pre-order checklist
0 / 5 complete
Quick knowledge check
What is the safest way to use a construction calculator?
Microlearning guide
Geometry is only one layer
A correct volume or spacing formula does not replace structural, hydraulic, product, or code requirements.
Rounding changes purchases
Whole bags, blocks, buckets, or units often require rounding up even when the mathematical result is fractional.
Assumptions drive results
Waste, density, coverage, capacity, and product dimensions can move an estimate more than extra decimal places.
Examples and practical uses
Early planning
Compare material or layout scenarios before requesting supplier quotes.
Purchase cross-check
Compare calculated quantities with package coverage, manufacturer capacity, or bulk-unit recommendations.
Measurement review
Use the formula table to independently reproduce the main calculation.
Related calculators
Frequently asked questions
Why subtract the pipe volume?
A pipe occupies part of the trench cross-section, so the tool subtracts its cylindrical volume from the gravel-filled trench volume.
Does the calculator include filter fabric?
No. Fabric is a surface-area material and should be measured separately with overlap and wrapping allowances.
Is the tons estimate exact?
No. It multiplies volume by the density you enter. Actual stone density varies by aggregate type, gradation, moisture, and supplier.
Does this design the French drain slope?
No. It estimates gravel quantity only. Pipe slope, outlet, soil conditions, and hydraulic capacity must be designed separately.
What if the pipe does not run the full trench?
Use the calculator as a first pass, or reduce the effective pipe length externally when making a more detailed estimate.