Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

DFU - Drainage Fixture Units

Sponsored Links

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.

A Fixture Unit is not a flow rate unit but a design factor based on the rate of discharge, time of operation and frequency of use of a fixture. A fixture unit is equal to one cubic foot of water drained in an 1 1/4 pipe over one minute (≈ 7.48 US gpm, ≈ 0.47 l/s).

DFU - Drainage Fixture Units
Individual Appliance, Appurtenance or FixtureMinimum Size of TrapDrainage Fixture Unit Values
Typical Values used in Europe
(inch)Private InstallationsPublic Installations(l/s)
Automatic clothes washers, commercial 2 3
Automatic clothes washers, residential 2 2
Bathroom (water closet, lavatory, bidet and tub or shower) 3 6 -
Bathtub 1 1/2 2 2 0.9
Bidet 1 1/4 1   0.3
Bidet 1 1/2 2  
Clothes Washer 2 3 3
Dental unit, cuspidor 1 1/4 1
Dental lavatory 1 1/2 1
Dishwashing machine, domestic 1 1/2 2 2 0.6
Drinking fountain 1 1/4 0.5 0.5 0.1
Floor drain, 3" 3 6 6
Floor drain, 4" 4 8 8 2
Food waste disposer 2 3
Shower 2 2 2 0.4
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
Mobile home, trap 3 12
Service or mop basin 2   3
Sink, bar 1 1/2 1 0.3
Sink, clinical 1 1/2 2
Sink, commercial with food waste 2 3
Sink, kitchen domestic 1 1/2 2 2 0.6
Sink, laundry 1 1/2 2 2
Sink, service mop basin 2 3 0.9
Urinal 2 2 2 0.3
Washfountain 1 1/2 2
WC - Water Closet, gravity tank 3 3 4 1.8
WC - Water Closet, flushometer tank, valve 3 3 4
Water cooler 1 1/4 0.5 0.5

Fixture Units are used in plumbing design for both water supply (WFSU) and waste water (DFU).

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.

Sponsored Links

Related Topics

Sanitary Drainage Systems

The purpose of the sanitary drainage system is to remove effluent discharged from plumbing fixtures and other equipment.

Related Documents

Cast Iron Soil Pipes - Dimensions

Dimensions of cast iron soil pipes.

Cleanouts in Draining Systems

Cleanouts provides access to the sewer for rodding.

Cold Water Dwellings - Storage Capacities

Required cold water dwelling storage capacity - commonly used fixtures and types of buildings.

Cold Water Storage per Occupant

Cold water storage for occupants in common types of buildings as factories, hospitals, houses and more

Draining Systems - Main Vents

Vents in draining systems protects traps against pressure differences that could cause them to siphon or blow out .

Drains and Sewers - Capacities vs. Size

Drainage Fixture Units (DFU) connected to building drains and sewers.

Fixtures Trap Sizes

Recommended drain trap sizes for different types of fixtures

Plumbing Codes

Plumbing or sanitation codes are a set of rules and regulations imposed by cities, counties or states.

Sanitary Drainage Systems - Volume Flow

Calculate expected volume flow load in sanitary drainage systems.

Sanitary Piping - Drainage Fixtures Unit Loads

Maximum Drainage Fixture Unit - DFU - loads in sanitary piping systems.

Sewer Pipes - Capacities vs. Slope

Carrying capacities of sewer and wastewater pipes - gpm and liter per second.

Trap Sizes vs. Fixture Units

No. of fixture units and required trap size.

Water Supply Fixture Units WSFU

WSFU is used to calculate water supply service systems.

Sponsored Links

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!


We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.