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IPC Ch.7
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact IPC Ch.7 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Drainage pipe sizing keeps waste moving by gravity without clogging or losing its trap seals. This app uses the IPC Chapter 7 method: total the drainage fixture units (DFU) on a branch or stack, then read the minimum pipe size and slope that carries them.
How it works
- Assign each fixture its DFU value (a toilet is 3–4, a lavatory 1, and so on).
- Total the DFU on the horizontal branch, the stack, and the building drain.
- Read the minimum pipe diameter for that DFU load at the chosen slope from the IPC tables.
Worked example
A bathroom group (toilet, lavatory, tub) totals about 5–6 DFU. That fits a 3-inch branch for the toilet, while a 2-inch line handles the tub and lavatory together within their DFU limit.
Related calculators
Set the fall with the drainage slope calculator and size venting with the trap and vent calculator.
Drainage pipe sizing FAQ
What is a drainage fixture unit?
A DFU is a normalized measure of the discharge load a fixture puts on the drainage system. The IPC assigns each fixture a DFU value, and pipe size is read from the total.
Does pipe size depend on slope?
Yes. A given pipe carries more DFU at a steeper slope. The app lets you pick the slope and returns the minimum diameter for that DFU load.
Branch, stack, and building drain?
All three. The app sizes horizontal branches, vertical stacks, and the building drain or sewer, each of which has its own DFU limits in the IPC.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Drainage Pipe Sizing on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.