01 / Fixtures & System
Total DFU
0
02 / Pipe Length & Gradient
Horizontal distance from highest fixture to point of connection.
WC pan limits: Max. 100 pans on DN 100 branch; max. 240 pans on DN 150 branch drain (NZS 3500.2 cl. 3.8.1). Engineering design required beyond these limits.
03 / Result
Pipe sizing — DFU capacity by pipe size
| Pipe Size (DN) | Max DFU | Min Grade | Max Length | Adequate? |
|---|
AS/NZS 3500.2:2021 / NZS 3500.2:2003 — scope and limitations. This tool applies the Discharge Fixture Unit (DFU) method for sizing sanitary drainage pipes within the scope of AS/NZS 3500.2 and NZS 3500.2. Systems with more than 240 WC pans, multi-storey stack connections, pumped discharge, or trade waste require specific engineering design per the relevant standard. Minimum cover for drainage pipes is 150 mm (NZS 3500.2 cl. 3.3). All drainage work must be designed and installed by a licensed drainlayer in accordance with NZBC G13.
Reference — DFU Values (AS/NZS 3500.2 Table 3.1 / NZS 3500.2 Table 1)
| Fixture | DFU | Connection Size |
|---|---|---|
| Water closet — flush tank | 3 | DN 100 |
| Water closet — flush valve | 6 | DN 100 |
| Urinal — per stall / basin | 2 | DN 40–50 |
| Bath (with or without shower) | 2 | DN 40 |
| Shower — without basin | 2 | DN 80 |
| Shower — with basin (combined) | 3 | DN 80 |
| Bidet | 1 | DN 40 |
| Hand wash basin / vanity | 1 | DN 40 |
| Kitchen sink (domestic) | 1.5 | DN 50 |
| Laundry tub / trough | 1.5 | DN 40 |
| Dishwasher (domestic) | 1 | DN 40 |
| Washing machine (to 6 kg) | 1 | DN 40 |
| Floor waste gully | 1 | DN 100 |
| Commercial kitchen sink | 3 | DN 50 |
For branched fixture groups, DFU totals from multiple fixtures are added before sizing. Fixture branches ≤ DN 80 may connect to DN 100 stacks.