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 the Uniform Plumbing Code (UPC), and can be used to determine the required drainage capacity from the fixtures and their service systems.

Individual Appliance, Appurtenance or Fixture Minimum Size 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  
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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