Guide Line for Sewer Systems
Content
Capacity of Sewer Pipes
Carrying capacity of sewer and wastewater pipes - gpm and liter per second
The diagrams below can be used for design of sewage and wastewater gravity conveying systems
where capacities in GPM or liter per second and the slopes of the pipe lines are known.
Sewage Pipe Capacity - Imperial units - gpm
Sewage Pipe Capacity - SI Units - liter per second
1 | Page
The table below indicates sewage pipe capacity in gpm:
Carrying Capacity of Sewer Pipe (gallons per minute)
Decline per 100 ft of pipe (ft)
Size of
pipe
(inches)
1
2
3
6
9
12
24
36
3
13
19
23
32
40
46
64
79
4
27
38
47
66
81
93
131
163
6
75
105
129
183
224
258
364
450
8
153
211
265
375
460
527
750
923
9
205
290
355
503
617
712
1006
1240
2 | Page
Carrying Capacity of Sewer Pipe (gallons per minute)
Decline per 100 ft of pipe (ft)
Size of
pipe
(inches)
1
2
3
6
9
12
24
36
10
267
378
463
655
803
926
1310
1613
12
422
596
730
1033
1273
1468
2076
2554
15
740
1021
1282
1818
2224
2464
3617
4467
18
1168
1651
2022
2860
3508
4045
5704
7047
24
2396
3387
4155
5874
7202
8303
11744
14466
27
4407
6211
7674
10883
13257
15344
21770
26622
30
5906
8352
10223
14298
17717
20204
28129
35513
36
9700
13769
16816
23760
29284
33722
47523
58406
The discharge rate is based on clean water and half filled pipes.
1 gal (US)/min = 6.30888x10-5 m3/s = 0.227 m3/h = 0.06309 dm3(liter)/s = 2.228x10-3 ft3/s =
0.1337 ft3/min = 0.8327 Imperial gal (UK)/min
Example - Capacity of Sewer Pipe
The capacity of a 4 inches sewer pipe with decline 12 ft per 100 ft pipe can be indicated from the
table above to 93 gpm.
Drainage Fixture Unit Loads for Sanitary Piping
Maximum Drainage Fixture Unit - DFU - Loads for sanitary piping
The maximum permissible Drainage Fixture Unit (DFU) loads for sanitary piping can be estimated
with the table below.
3 | Page
Maximum Drainage Fixture Units - Stacks and Horizontal Fixture Branches
Maximum Drainage Fixture Units (DFU)
Pipe Size
Horizontal
fixture
branch
Stacks less
than 3
stories in
height
NPS
(inches)
DN
(mm)
1 1/20)
40
3
20)
50
2 1/20)
Stacks more than 3
stories high
Total for
stack
Total for one
story
4
8
2
6
10
24
6
65
12
20
42
9
3
80
201)
481)
722)
201)
4
100
160
240
500
90
5
125
360
540
1100
200
6
150
620
960
1900
350
0)
No water closet permitted
1)
Maximum two water closets
2)
Maximum six water closets
Maximum Drainage Fixture Units - Building Drains and Building Drain Branches from
Stacks
Maximum Drainage Fixture Units (DFU)
Pipe Size
4 | Page
Slope in/ft (cm/m)
NPS
(inches)
DN
(mm)
1/4 (2.1)
1/2 (4.2)
20)
50
21
26
Maximum Drainage Fixture Units (DFU)
Pipe Size
Slope in/ft (cm/m)
NPS
(inches)
DN
(mm)
1/4 (2.1)
1/2 (4.2)
2 1/20)
65
24
31
3
80
421)
501)
4
100
216
250
5
125
480
575
6
150
840
1000
Drainage Fixture Unit Values (DFU)
DFU are used to determine the drainage from fixtures and the necessary capacity
of the sewer service systems
The Drainage Fixture Unit Values (DFU) are defined by the Uniform Plumbing Code (UPC), and can
be used to determine the required drainage capacity from the fixtures and their service systems.
Minimum Size
Individual Appliance,
Appurtenance or Fixture
5 | Page
Drainage Fixture Unit Values
(DFU)
(inch)
Private
Installations
Public
Installations
Bar sink
1 1/2
1
1
Bathroom (water closet,
lavatory, bidet and tub or
shower)
3
6
-
Bathtub
1 1/2
2
2
Bidet
1 1/4
1
Minimum Size
Individual Appliance,
Appurtenance or Fixture
Drainage Fixture Unit Values
(DFU)
(inch)
Private
Installations
Public
Installations
Bidet
1 1/2
2
Clothes Washer
2
3
3
Dishwasher, domestic
1 1/2
2
2
Drinking fountain
1 1/4
0.5
0.5
Floor drain
2
2
2
Shower
2
2
2
Laundry tub
1 1/2
2
2
Lavatory
1 1/4
1
1
Bar sink
1 1/2
1
Kitchen sink, domestic
1 1/2
2
2
Laundry sink
1 1/2
2
2
Service or mop basin
2
Urinal
2
2
2
Water closet with gravity tank
3
3
4
Water closet with flushometer
tank
3
3
4
3
1 WFSU = 1 GPM = 3.79 liter/min
Note that this conversion is only true for one or a few fixtures. Since the fixtures in a system are
never used all at the same time, the total units (capacity) achieved by adding the numbers for all
6 | Page
fixtures must be compensated for intermittent use if we want a realistic estimate of the total drainage
load.
Expected Loads in Sanitary Drainage Systems
Calculate expected loads in sanitary drainage systems
The total theoretical load for a sanitary drainage system can be calculated by adding all fixtures
known maximum loads. Due to the nature of intermittent use the number of fixtures will unfortunate
add up to unrealistic loads for the main drainage lines to handle. Realistic loads will always be far
less than the total theoretical loads.
An expected load for a sanitary drainage system can be estimated using the empirical formula like
qet = k ( Σqn )1/2
(1)
where
qet = expected total drainage load (gpm, l/s)
k = system coefficient describing the nature of the system
Σqn = total theoretical load - all fixtures summarized (gpm, l/s)
Note that the minimum expected total load can never be less than the load from the largest fixture.
The system coefficient is used to compensate the calculation to the nature of the system. For
systems typical serving large groups of people where the use is intermittent, like
hotels
hospitals
schools
theaters
wardrobes in factories
etc
the coefficient - k - should be in the range 0.5 - 0.8. Closer to 0.8 for smaller systems with few fixtures
and closer to 0.5 for larger systems with many fixtures.
For more ordinary systems where consumption patterns are more continuously like
homes
offices
7 | Page
nursing homes
the coefficient - k - should be in the range 0.3 - 0.6. Closer to 0.3 for larger systems with many
fixtures and closer to 0.6 for smaller systems with few fixtures.
Example - Sanitary Drainage System Hospital
If the theoretical loads from the fixtures in a smaller hospital adds up to 50 l/s, the expected load can
be estimated to
qet = 0.7 (50 l/s)1/2
= 4.9 l/s
Assuming this is a smaller hospital the coefficient can be set to 0.7.
8 | Page
Carrying capacity of sewer and wastewater pipes - gpm and liter per second
The diagrams below can be used for design of sewage and wastewater gravity conveying systems
where capacities in GPM or liter per second and the slopes of the pipe lines are known.
Sewage Pipe Capacity - Imperial units - gpm
Sewage Pipe Capacity - SI Units - liter per second
1 | Page
The table below indicates sewage pipe capacity in gpm:
Carrying Capacity of Sewer Pipe (gallons per minute)
Decline per 100 ft of pipe (ft)
Size of
pipe
(inches)
1
2
3
6
9
12
24
36
3
13
19
23
32
40
46
64
79
4
27
38
47
66
81
93
131
163
6
75
105
129
183
224
258
364
450
8
153
211
265
375
460
527
750
923
9
205
290
355
503
617
712
1006
1240
2 | Page
Carrying Capacity of Sewer Pipe (gallons per minute)
Decline per 100 ft of pipe (ft)
Size of
pipe
(inches)
1
2
3
6
9
12
24
36
10
267
378
463
655
803
926
1310
1613
12
422
596
730
1033
1273
1468
2076
2554
15
740
1021
1282
1818
2224
2464
3617
4467
18
1168
1651
2022
2860
3508
4045
5704
7047
24
2396
3387
4155
5874
7202
8303
11744
14466
27
4407
6211
7674
10883
13257
15344
21770
26622
30
5906
8352
10223
14298
17717
20204
28129
35513
36
9700
13769
16816
23760
29284
33722
47523
58406
The discharge rate is based on clean water and half filled pipes.
1 gal (US)/min = 6.30888x10-5 m3/s = 0.227 m3/h = 0.06309 dm3(liter)/s = 2.228x10-3 ft3/s =
0.1337 ft3/min = 0.8327 Imperial gal (UK)/min
Example - Capacity of Sewer Pipe
The capacity of a 4 inches sewer pipe with decline 12 ft per 100 ft pipe can be indicated from the
table above to 93 gpm.
Drainage Fixture Unit Loads for Sanitary Piping
Maximum Drainage Fixture Unit - DFU - Loads for sanitary piping
The maximum permissible Drainage Fixture Unit (DFU) loads for sanitary piping can be estimated
with the table below.
3 | Page
Maximum Drainage Fixture Units - Stacks and Horizontal Fixture Branches
Maximum Drainage Fixture Units (DFU)
Pipe Size
Horizontal
fixture
branch
Stacks less
than 3
stories in
height
NPS
(inches)
DN
(mm)
1 1/20)
40
3
20)
50
2 1/20)
Stacks more than 3
stories high
Total for
stack
Total for one
story
4
8
2
6
10
24
6
65
12
20
42
9
3
80
201)
481)
722)
201)
4
100
160
240
500
90
5
125
360
540
1100
200
6
150
620
960
1900
350
0)
No water closet permitted
1)
Maximum two water closets
2)
Maximum six water closets
Maximum Drainage Fixture Units - Building Drains and Building Drain Branches from
Stacks
Maximum Drainage Fixture Units (DFU)
Pipe Size
4 | Page
Slope in/ft (cm/m)
NPS
(inches)
DN
(mm)
1/4 (2.1)
1/2 (4.2)
20)
50
21
26
Maximum Drainage Fixture Units (DFU)
Pipe Size
Slope in/ft (cm/m)
NPS
(inches)
DN
(mm)
1/4 (2.1)
1/2 (4.2)
2 1/20)
65
24
31
3
80
421)
501)
4
100
216
250
5
125
480
575
6
150
840
1000
Drainage Fixture Unit Values (DFU)
DFU are used to determine the drainage from fixtures and the necessary capacity
of the sewer service systems
The Drainage Fixture Unit Values (DFU) are defined by the Uniform Plumbing Code (UPC), and can
be used to determine the required drainage capacity from the fixtures and their service systems.
Minimum Size
Individual Appliance,
Appurtenance or Fixture
5 | Page
Drainage Fixture Unit Values
(DFU)
(inch)
Private
Installations
Public
Installations
Bar sink
1 1/2
1
1
Bathroom (water closet,
lavatory, bidet and tub or
shower)
3
6
-
Bathtub
1 1/2
2
2
Bidet
1 1/4
1
Minimum Size
Individual Appliance,
Appurtenance or Fixture
Drainage Fixture Unit Values
(DFU)
(inch)
Private
Installations
Public
Installations
Bidet
1 1/2
2
Clothes Washer
2
3
3
Dishwasher, domestic
1 1/2
2
2
Drinking fountain
1 1/4
0.5
0.5
Floor drain
2
2
2
Shower
2
2
2
Laundry tub
1 1/2
2
2
Lavatory
1 1/4
1
1
Bar sink
1 1/2
1
Kitchen sink, domestic
1 1/2
2
2
Laundry sink
1 1/2
2
2
Service or mop basin
2
Urinal
2
2
2
Water closet with gravity tank
3
3
4
Water closet with flushometer
tank
3
3
4
3
1 WFSU = 1 GPM = 3.79 liter/min
Note that this conversion is only true for one or a few fixtures. Since the fixtures in a system are
never used all at the same time, the total units (capacity) achieved by adding the numbers for all
6 | Page
fixtures must be compensated for intermittent use if we want a realistic estimate of the total drainage
load.
Expected Loads in Sanitary Drainage Systems
Calculate expected loads in sanitary drainage systems
The total theoretical load for a sanitary drainage system can be calculated by adding all fixtures
known maximum loads. Due to the nature of intermittent use the number of fixtures will unfortunate
add up to unrealistic loads for the main drainage lines to handle. Realistic loads will always be far
less than the total theoretical loads.
An expected load for a sanitary drainage system can be estimated using the empirical formula like
qet = k ( Σqn )1/2
(1)
where
qet = expected total drainage load (gpm, l/s)
k = system coefficient describing the nature of the system
Σqn = total theoretical load - all fixtures summarized (gpm, l/s)
Note that the minimum expected total load can never be less than the load from the largest fixture.
The system coefficient is used to compensate the calculation to the nature of the system. For
systems typical serving large groups of people where the use is intermittent, like
hotels
hospitals
schools
theaters
wardrobes in factories
etc
the coefficient - k - should be in the range 0.5 - 0.8. Closer to 0.8 for smaller systems with few fixtures
and closer to 0.5 for larger systems with many fixtures.
For more ordinary systems where consumption patterns are more continuously like
homes
offices
7 | Page
nursing homes
the coefficient - k - should be in the range 0.3 - 0.6. Closer to 0.3 for larger systems with many
fixtures and closer to 0.6 for smaller systems with few fixtures.
Example - Sanitary Drainage System Hospital
If the theoretical loads from the fixtures in a smaller hospital adds up to 50 l/s, the expected load can
be estimated to
qet = 0.7 (50 l/s)1/2
= 4.9 l/s
Assuming this is a smaller hospital the coefficient can be set to 0.7.
8 | Page
