Septic Drainfield Trench Length

Required absorption area and trench linear feet from design daily flow and the application rate set by your local code.

Run the calculator

Example

You enter

Design daily flow (gpd) 600
Application rate (gpd / ft²) 0.6
Trench width (ft) 3

You get

Required absorption area 1000 ft²
Trench linear feet 333.3 ft

Details, formula, and sources

Required absorption area = design_daily_flow_gpd / application_rate_gpd_per_ft². Trench feet = required_area / trench_width_ft.

U.S. EPA Onsite Wastewater Treatment Systems Manual (EPA/625/R-00/008) by name; per-state and per-county application rates set by local code (not bundled).

Free at epa.gov/septic. State application-rate tables free on each state department of health / DEQ site.

Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

Field names used by the API: design_flow_gpd, application_rate_gpd_per_ft2, trench_width_ft, required_area_ft2, trench_feet

Application rate user-supplied from local code (this tool deliberately does not bundle a per-state shard)local AHJ