TradeToolsPlumbing · in the TradeTools app
Fixture Unit Calculator
The water supply fixture units and drainage fixture units a set of fixtures adds up to — the two totals every supply-pipe and drain-sizing table starts from.
IPC Table 709.1 · Appendix E Table E103.3(2)
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Worked example
Two full baths, a kitchen and a laundry — how many fixture units?
| Bathroom Group, private (flush tank WC) | 2 |
|---|---|
| Kitchen Sink, private (faucet) | 1 |
| Dishwasher, private (automatic) | 1 |
| Clothes Washer, private (8 lb) | 1 |
| Laundry Tray (1 to 3 compartments) | 1 |
| Supply fixture units | 12.8 |
|---|---|
| Drainage fixture units | 18.0 |
| Fixtures | 6 |
Table E103.3(2) gives a private bathroom group with a flush-tank water closet 3.6 WSFU (total column, hot and cold together) and the sink, dishwasher, washer and laundry tray 1.4 each: 2 × 3.6 + 4 × 1.4 = 12.8. Table 709.1 gives the bathroom group 5 DFU and the other four 2 each: 10 + 8 = 18.
How it's calculated
The table behind the number
Each fixture in the list carries two printed values: the water supply fixture units of IPC Appendix E, Table E103.3(2), taken from the total column for its occupancy and supply control (private, flush tank), and the drainage fixture units of IPC Table 709.1. The app multiplies each by its count and adds them up. Fixtures the printed table does not list — a hose bibb, a bar sink — are assigned by comparison, as the table note instructs, and are marked as such in the list. The values are the same in the 2018, 2021 and 2024 editions.
- IPC Appendix E, Table E103.3(2)Load values assigned to fixtures, in water supply fixture units — total column (bathroom group with flush-tank WC 3.6; kitchen sink 1.4; lavatory 0.7; water closet, flush tank 2.2)
- IPC Table 709.1Drainage fixture units for fixtures and groups (bathroom group with 1.6 gpf WC 5; kitchen sink 2; lavatory 1; water closet, 1.6 gpf, 3)
Questions
Before you trust the number
Bathroom group, or the fixtures one by one?
Use the group when a water closet, lavatory and bathtub or shower share one bathroom: the tables give the group its own, smaller value — 3.6 WSFU and 5 DFU for a flush-tank bathroom — because those fixtures are not all used at once. Listed separately the same three would sum to 4.3 WSFU and 6 DFU.
What do I do with the totals?
Size the pipes. Water supply fixture units go to Table E201.1 for the meter and distribution pipe size by pressure range and developed length (Water Pipe Sizing in the app), or through Table E103.3(3) to a demand in gallons per minute (Building Water Demand); drainage fixture units go to Tables 710.1(1) and 710.1(2) for the building drain, branches and stacks (Drain Sizing). This one gives the totals those start from.
Public or private?
Private is a dwelling, or a private bathroom in a hotel or office — one household's use. Public lavatories, water closets and showers carry higher supply values (a public lavatory 2.0 WSFU against 0.7 private) because they see continuous use. Pick the row that matches the occupancy.