Measure trench length, width, and rock depth.
Enter trench length, trench width, and rock depth to estimate clean drainage aggregate. Enter the pipe diameter and count so cylindrical pipe displacement is removed automatically.
Verified formulaEditable presetsUS + metric
Purpose-built estimator
Project measurements
Total length of the gravel-filled trench.
Inside trench width filled with rock.
Depth of rock inside the trench.
Outside diameter of pipe inside the rock zone.
Count of pipes running through the trench.
Bulk density for clean drainage rock.
Percent added for cuts, spillage, edge cleanup, and small estimating errors.
Optional supplier price used to estimate material cost before delivery fees and taxes.
Drain trench cross-section
- 1Filter fabric
- 2Clean drain rock
- 3Perforated pipe
- 4Sloped trench
How to use this calculator
Read full measuring guide Measure, verify, and order
Measure the trench as a rectangular rock zone, then subtract the round pipe space.
Enter pipe diameter and pipe count.
Review net rock after pipe displacement.
What each input means
Trench length
Total length of the gravel-filled trench.
Unit: ft or m. Measure the centerline of the trench route.Trench width
Inside trench width filled with rock.
Unit: in or cm. Measure wall to wall after excavation.Rock fill depth
Depth of rock inside the trench.
Unit: in or cm. Measure from trench bottom to top of rock fill.Pipe diameter
Outside diameter of pipe inside the rock zone.
Unit: in or cm. Use pipe outside diameter or nominal diameter as a planning value.Number of pipes
Count of pipes running through the trench.
Unit: count. Enter 0 for no pipe displacement.Drain-rock density
Bulk density for clean drainage rock.
Unit: lb/ft3 or kg/m3. Use supplier density for washed stone.Extra / waste
Percent added for cuts, spillage, edge cleanup, and small estimating errors.
Unit: percent. Use 5 percent for simple square work and 10 percent or more for irregular work.Price per ton
Optional supplier price used to estimate material cost before delivery fees and taxes.
Unit: USD per US ton. Enter the quoted material price per US short ton. Leave 0 if you only need quantity.Check the calculation
Example: a 50 ft trench, 12 inches wide, and 12 inches deep loses the volume occupied by a 4 inch pipe.
A 50 ft trench, 1 ft wide, and 1 ft deep holds 1.85 cubic yards before allowances.
Total loose order 1.86 cu yd Total weight 2.51 US tons
Rock volume = trench length x width x fill depth - pipe cylinder volume.
Assumptions to check
- Use washed, clean stone that meets the drainage design.
- The calculator treats the trench as a rectangular volume.
- Confirm slope, pipe, fabric, and outlet requirements separately.
- Does not design hydraulic capacity.
- Does not verify outlet or slope.
- Jagged trench walls may need more waste.
Read our formulas, sources, image credits, and review policy
Frequently Asked Questions
What does this drain rock and trench calculator calculate?
It uses project-specific inputs and the formula shown below. Rock volume = trench length x width x fill depth - pipe cylinder volume.
Are the presets exact specifications?
No. Presets are editable planning starting points. Confirm depths, materials, and densities with the supplier, manufacturer, or project designer.
Why can delivered weight differ?
Bulk density varies by supplier and moisture level. Moisture, gradation, compaction, and scale accuracy can change the delivered weight.