Below-Grade Drainage Calculator

Drain tile sizing from water table and soil permeability.

Foundation perimeter (ft)

Foundation depth (ft)

Water table depth (ft)

Soil type (1=gravel, 2=sand, 3=silt, 4=clay)

Trench width (ft)

Design rainfall (in/hr)

Tab to move between fields

Design flow rate (GPM)

8.73

Pipe diameter (inches)4

Drainage gravel (tons)74.1

Gravel volume (cu yd)52.9

Filter fabric (sq ft)2,220

Drainage board (sq ft)960

Estimated material cost ($)$4,769.00

Soil NameSilt

How to Use This Calculator

Enter Foundation Perimeter (ft) — the total linear feet of foundation wall requiring a drainage system.
Input Foundation Depth (ft) and Water Table Depth (ft) to determine the hydraulic head the system must manage.
Select Soil Type (1=gravel, 2=sand, 3=silt, 4=clay) — clay soils require larger pipe and more gravel than sandy soils.
Enter Trench Width (ft) and Design Rainfall (in/hr) from your local 10-year, 1-hour storm intensity map.
Review Design Flow Rate (GPM) and Recommended Pipe Diameter to specify perforated drain pipe.
Use Drainage Gravel (tons), Filter Fabric (sq ft), and Estimated Material Cost for procurement and bid preparation.

How the result changes with Foundation perimeter (ft)

Foundation perimeter (ft): Total linear feet of foundation perimeter requiring drainage.
Foundation depth (ft): Depth of foundation below grade to bottom of footing.
Water table depth (ft): Seasonal high water table depth below grade. 0 = at surface.
Soil type (1=gravel, 2=sand, 3=silt, 4=clay): Predominant soil type affects drainage rate. Clay requires more drainage capacity.
Trench width (ft): Width of drainage trench around foundation. Typically 12-24 inches.
Design rainfall (in/hr): Design storm rainfall intensity. Use local 10-year, 1-hour value.

Design flow rate (GPM): Combined groundwater seepage + surface water flow in gallons per minute.
Pipe diameter (inches): Recommended perforated drain pipe diameter.
Drainage gravel (tons): Clean washed gravel needed for drain trench backfill.
Gravel volume (cu yd): Gravel volume in cubic yards.
Filter fabric (sq ft): Geotextile filter fabric to wrap drain trench.
Drainage board (sq ft): Dimpled drainage board area for foundation walls.
Estimated material cost ($): Approximate material costs for pipe, gravel, fabric, and drainage board.

Identify Input Parameters
4 parameters
Foundation perimeter (ft) = 120, Foundation depth (ft) = 8, Water table depth (ft) = 6, Soil type (1=gravel, 2=sand, 3=silt, 4=clay) = 3 = 6 input(s) provided
Calculate Design flow rate
Design flow rate = (totalFlowPerDay * 7.48052) / (24 * 60)
8.73 = 8.73
Calculate Pipe diameter
Pipe diameter
4 = 4
Calculate Drainage gravel
Drainage gravel = (gravelVolumeCuFt / 27) * 1.4
74.1 = 74.1