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Sewage System Sizing

Research has shown that additional plumbing fixtures, such as separate showers with whirlpool tubs instead of tub/shower combinations, double lavatories, bidets, etc., increase the amount of wastewater generated by a home. Any two additional fixtures may increase septic tank and/or drainfield sizes. If you may be installing several fixtures, an early consultation with our Sanitarians can identify the proper sizing of the septic tanks and drainfield. 

Keep in mind:

  • The listed sizes are for primary drainfield areas. The total drainfield area required is the sum of the primary and reserve areas. The reserve area is 1.5 times that of the primary drainfield.
  • Effluent filters are highly recommended and may be required on certain sites and on alternative on-site sewage systems. Effluent filters remove small solid particles from wastewater leaving the septic tank, preventing the particles from entering the drainfield. Refer to the manufacturer's recommendations for use and maintenance.
  • A study, den, or similar room which may be converted into a bedroom must be included in the total number of bedrooms.

Number of
Bedrooms

Total Septic
Tank Capacity

Drainfield Size
(Coarse Sand/Gravel)

Drainfield Size
(Clean Medium Sand)

Drainfield Size
(Fine/Loamy Sand)

Drainfield Size
(Fill-Type Drainfield)

2 or less

1500 gallons

800 sq. ft.

1000 sq. ft.

1500 sq. ft.

2500 sq. ft.

3

2000 gallons

1000 sq. ft.

1200 sq. ft.

1800 sq. ft.

2880 sq. ft.

4

2500 gallons

1200 sq. ft.

1600 sq. ft.

2000 sq. ft.

3200 sq. ft.

5

3000 gallons

1600 sq. ft.

1800 sq. ft.

2200 sq. ft.

3200 sq. ft.

6

3500 gallons

1800 sq. ft.

2000 sq. ft.

2500 sq. ft.

3800 sq. ft.


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