Septic Tank Capacity Estimator
Create a preliminary septic-tank capacity estimate from occupants, bedrooms, daily wastewater, retention time, reserve and available tank increments.
Default project preview
1,250 gallons
Estimated daily flow
240 gal/day
Retention volume
480 gal
Bedroom allowance
900 gal
Design volume before rounding
1,125 gal
Calculator
Build the material order
Your order will appear here
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.
Occupancy volume = occupants × daily flow × retention days. Bedroom allowance is calculated separately. The larger value receives reserve, then rounds up to an available tank increment.
FAQ
Septic Tank Capacity Estimator questions
Why compare occupancy and bedroom allowances?+
Some planning methods consider expected flow while local rules may also use bedroom-based minimums.
Is this an approved septic design?+
No. Tank and drain-field design requires site evaluation, soil data, permits and local regulatory criteria.
Does a larger tank fix an undersized drain field?+
No. Tank capacity and soil-treatment capacity are different parts of the system.