FIXTURE UNIT & VENTING CALCULATOR

Based on the Australian Plumbing Standards

Select the number of each fixture to calculate the total fixture units (FU) for your plumbing system. Fixture units are used to size drains, waste pipes, and vents to ensure the drainage system works correctly.

Your Fixtures

Toilet

4 FU

0
Hand Basin
1 FU

0
Bath
4 FU

0
Bath (shower combo)

Bath tub with shower over it

4 FU

0
Shower

Count each shower head separately

2 FU

0
Bidet / Bidette
1 FU

0
Laundry Trough

If a washing machine connects to a laundry trap, only the laundry fixture unit rating applies.

5 FU

0
Kitchen Sink

With or without disposal unit. If a dishwasher connects to the sink trap, only the sink FU rating applies.

3 FU

0
Bar / Tea Sink

Domestic

1 FU

0
Dishwasher

Domestic only. If the waste pipe connects to a kitchen sink, only the kitchen sink FU rating applies.

3 FU

0
Clothes Washing Machine

Domestic only. If the waste pipe connects to a laundry trough, only the trough FU rating applies.

5 FU

0
Floor Waste Gully

When a floor waste gully has fixtures connected into it, its fixture unit rating is simply the total of all those fixtures added together.

0 FU

0

Total Fixture Units:

Commercial & Medical Fixtures

Pot / Utility Sink
5 FU

0
Ablution Trough
3 FU

0
Drinking Fountain
1 FU

0
Urinal — Wall-hung / Waterless

Count each urinal

1 FU

0
Urinal — Stall

Per 600mm of slab length

1 FU

0
Autopsy Table
3 FU

0
Bain-nurse
1 FU

0
Bedpan Sterilizer
4 FU

0
Bedpan Washer DN80

4 FU

0
Bedpan Washer DN100

4 FU

0
Bedpan Washer/Sterilizer DN80

4 FU

0
Bedpan Washer/Sterilizer DN100

4 FU

0
Circular Wash Fountain
4 FU

0
Dental Unit
1 FU

0
Glass-Washing Machine
3 FU

0
Potato Peeler
3 FU

0
Sanitary Napkin Disposal Unit
3 FU

0
Bar Sink — Commercial
1 FU

0
Sink Cleaner
1 FU

0
Sink Laboratory
1 FU

0
Slop Hopper

4 FU

0
Combination Pan Room Sink DN80

4 FU

0
Combination Pan Room Sink DN100

4 FU

0

Commercial Subtotal:

0 FU

Bathroom Group 6 FU per group

Basin + bath + shower + toilet in one room

6 FU

0

Bathroom Group Rule — If a single bathroom contains a hand basin, bath, shower AND toilet all in the same room, count it as just 6 FU total using the 'Bathroom Group' row above, instead of adding each fixture up separately.

Results

Total Fixture Units

—

Minimum Vent Pipe Size

—

Minimum Main Drain Size

—

Based on minimum grade per AS 3500.2

Vent Size Guide

Total Fixture Units	Vent Pipe Size
1 – 9 FU	40mm
10 – 29 FU	50mm
30 – 174 FU	65mm
175 – 399 FU	80mm
400 – 600 FU	100mm

Where two or more vents are connected to a drain, you can use smaller vents provided their combined vent ratings equal or exceed the single vent requirement.

How Many Fixture Units Can My Drain Handle?

These figures are for drains laid at the minimum allowable grade. A steeper fall means your drain can handle more fixture units.

Drain Size	Minimum Grade	Max Fixture Units
65mm	2.50%	25 FU
80mm	1.65%	61 FU
100mm	1.65%	165 FU
125mm	1.25%	425 FU
150mm	1.00%	855 FU
225mm	0.65%	3,250 FU
300mm	0.40%	6,780 FU

The minimum size for a main drain is 100mm.

The minimum size for a branch drain is 65mm.

Unvented Drain Rules

• A 65mm unvented drain can carry up to 5 fixture units — but not if there's a toilet or slop hopper. If all fixtures connect through a single floor waste, it can carry up to 10 FU.

• An 80mm unvented drain can carry up to 12 fixture units (maximum 1 toilet or slop hopper).

• A 100mm unvented drain can carry up to 30 fixture units (maximum 2 toilets or slop hoppers).

• An unvented drain must be no longer than 10 metres from the vented part of the system to the trap.

Minimum Vent Size Rules

• The vent connected to your main drain must be at least 50mm.

• The vent on any branch drain must be at least 40mm.

• Any drain that a vent is connected to must be at least 65mm.

back to plumbing calculators