Dry Well Size Calculator
Estimate runoff storage, aggregate-pit volume, footprint and modular dry-well quantity from catchment area, rainfall, capture target and editable void ratio.
Default project preview
336.6 gal
Event runoff
673.2 gal
Aggregate pit volume
4.17 yd³
Pit footprint
28.1 ft²
Modular units
7
Calculator
Build the material order
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Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Runoff = catchment area × rainfall depth × runoff coefficient. Target storage applies the capture percentage. Aggregate pit volume divides storage by void ratio; footprint divides by usable depth.
FAQ
Dry Well Size Calculator questions
Why is the aggregate pit larger than the water volume?+
Stone occupies part of the excavation, so only the void spaces store water.
Does this account for infiltration during the storm?+
No. It conservatively compares static storage and does not model infiltration or routing.
Where should overflow go?+
Overflow needs a safe, project-specific route that does not damage buildings or neighboring property.