In this article, we will explain how to determine the required size of a septic tank.  The typical residential septic tank size require...

Septic Tank Size Requirements all details you want to know it

In this article, we will explain how to determine the required size of a septic tank. The typical residential septic tank size required for a given average daily sewage wastewater flow in gallons is provided in a table of septic tank sizes. This article also explains how to calculate septic tank volume based on a septic tank inside dimensions measured in feet.
Required Septic Tank Size for Daily Water
Usage Volume in Gallons
Average Sewage            Minimum Septic Tank Size In Gallons       
Wastewater                    Of  Effective Capacity Needed (1)
Flow – Gallons Per
0-500                              900
601-700                          1200
801-900                          1500
1001-1240                      1900
2001-2500                      3200
4501-5000                      5800
Septic Tank in Gallons Size Based on Number of Bedrooms
0-2 bedrooms 750 gal. (2)
3 bedrooms 1000 gal.
4 bedrooms 1200 gal.
5-6 bedrooms 1500 gal.
Calculating Septic Tank Capacity in Gallons
Round SepticTanks
3.14 x radius squared x depth (all in feet) = cubic capacity. Cubic capacity x 7.5 = gallons capacity.
Rectangular Septic Tanks
Length x Width x Depth in feet x 7.5 = gallons
Rectangular Septic Tanks
(alternative method 1)
Length x width in inches / 231 = gallons per inch of septic tank depth. Multiply this number by septic tank depth in inches to get gallons
Rectangular Septic Tanks
(alternative method 2)
Length x Width x Depth in feet / .1337 = gallons
COMPUTING EXAMPLE – An Example of Computing Septic Tank Size, Capacity or
Volume in Gallons
One gallon of water has a volume of .1337 cubic feet. For a rectangular septic tank, multiply depth (or inside
“height”) in feet times width times length. Divide this figure by .1337 to establish the number of gallons in
the septic tank.
Example: How many gallons is held in a 4ft. deep x 5ft. wide x 8 ft. long septic tank? If the tank
dimensions were 4ft. x 5ft. x 8ft. = 160 cubic feet. Using the conversion factor to convert cubic feet to
gallons, 160 / .1337 = 1196 – or about a 1200-gallon tank.
One cubic foot of volume can contain 7.481 gallons of liquid. So a second approach to calculating septic
tank actual size or capacity in gallons is to multiply the septic tank volume in cubic feet by this constant,
which we round up to 7.5 gallons/cubic foot.

Plumbing - Calculation of Septic Tank Size


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