Fixture Unit Calculator
In the workshopDFU load & drain pipe size
Store name: “Fixture Unit Calculator: DWV”
Coming soon
Not out yet — but it’s close.
What size drain pipe do I need for these fixtures?
- IPC: DFU values from Table 709.1; drain sizing from Table 710.1(1) for building drains and sewers by slope, and Table 710.1(2) for horizontal branches and stacks
- UPC: DFU values from Table 702.1; drain sizing from Table 703.2 for horizontal and vertical drainage
- Size the pipe you mean: horizontal branch, soil or waste stack, or building drain and sewer under the IPC; horizontal or vertical drainage under the UPC, with a ⅛, ¼ or ½ inch-per-foot slope for the building drain
- A water-closet floor: a drain that serves a toilet is never sized below 3 inches, whatever the fixture-unit math says
What it is
What size drain pipe do these fixtures need? Add the fixtures in the system — toilets, lavatories, tubs, showers, sinks, washers, floor drains, urinals — and it tallies the drainage fixture units, then looks up the minimum pipe size the code requires. Pick a size yourself and it returns PASS or OVER CAPACITY on the spot, with a load bar, the DFU headroom left, and how full the pipe is as a percent.
Why we built it
It answers against the IPC or the UPC, never blended, and names the table the answer came from. The two codes rate some fixtures differently — a clothes washer is 2 DFU in the IPC but 3 in the UPC, a urinal 4 against 2, a service sink 2 against 3 — so the toggle actually changes the answer. The tables are transcribed straight from the IPC and UPC; it is a reference and planning tool, not the code book and not an engineered design, so confirm against the edition your AHJ enforces.
Want one like this?
Fixture Unit Calculator is one of 28. We can build yours.
Every app on the shelf started as one honest problem, scoped small and built native, end to end. That’s exactly how we approach client work — designed, built and shipped, without the bloat.
