Drainage Fixture Unit Values - DFU

DFU are used to determine the drainage from fixtures and required capacity of sewer service systems

DFU (Drainage Fixture Unit Values) is defined by the the Uniform Plumbing Code (UPC) and can be used to determine required drainage capacities from fixtures and their service systems.

Individual Appliance, Appurtenance or FixtureMinimum SizeDrainage Fixture Unit Values
(DFU)
(inch)Private InstallationsPublic 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  
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   3
Urinal 2 2 2
Water closet with gravity tank 3 3 4
Water closet with flushometer tank 3 3 4
  • 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 fixtures must be compensated for intermittent use if we want a realistic estimate of the total drainage load.

Related Topics

  • Water Systems - Hot and cold water systems - design properties, capacities, sizing and more

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