DFU Chart — Drainage Fixture Units & Minimum Trap Sizes

• aTraps larger than 3" fall under the trap-size table of IPC 709.2.
• bAn overhead shower or whirlpool attachment on a bathtub does not add DFU — the bathtub value already covers it.
• cUnlisted fixtures and devices with intermittent flow are computed under IPC 709.2 through 709.4.1.
• dTrap size matches the fixture outlet size rather than a fixed minimum.
• eWater closets and urinals cannot be counted at a lower DFU on building drains and sewers unless the lower value is confirmed by testing.
• fExtra fixtures added to a bathroom group add their own DFU on top of the group value.
• gClothes-washer standpipe drain, branch, and stack sizing follows IPC 406.2 (numbered 406.3 before the 2021 edition).
• hFloor sinks and other waste receptors are sized as receptors under IPC 709.4 and 709.4.1 for the fixtures draining into them.

• 1Indirect waste receptors are sized from the total drainage capacity of the fixtures discharging into them, per the UPC indirect-waste tables.
• 2Requires a 2" minimum drain even where the trap is smaller.
• 3Covers low-demand indirect waste such as refrigerators, coffee urns, and water stations.
• 4Covers moderate- and heavy-demand indirect waste such as commercial sinks and dishwashers.
• 5Where three or more clothes washers share drainage, each counts 6 fixture units when sizing the common drain.
• 6Water closets count as 6 fixture units when sizing septic tanks.
• 7Traps must not be oversized to the point the fixture discharge can no longer scour the trap.
• 8The assembly column applies to public assembly occupancies.
• 9A bathtub replaced by a shower no larger than 36" × 60" may keep its 1-1/2" trap and trap arm (2021 addition).

Find each fixture on the branch, stack, or drain you're sizing, take its DFU value, and add them up — the total is what the drain-sizing tables key on. Watch the private/public split on water closets: "private" means dwellings and similar single-user settings, while anything with open or semi-public use reads from the public row. The fixture unit calculator runs the count for you fixture by fixture.

The minimum trap column is the smallest trap (and fixture drain) the code allows for that fixture — a fixture can never drain through piping smaller than its trap. The two codes structure this differently: the IPC bakes private/public into the fixture rows, while the UPC rates each fixture across three occupancy columns — private, public, and assembly (public assembly occupancies, note 8) — and lists some fixtures on multiple rows by trap size. Under the UPC, read down the column matching the building's use.

The IPC (ICC) and UPC (IAPMO) assign different DFU values to the same fixtures and pair them with different sizing tables, so a fixture count is only meaningful inside one code family. Before you count, confirm which family your state or city enforces — and then check its amendments, because plumbing is one of the most heavily locally amended trades. Chicago, New York City, and several states rewrite fixture-unit rows outright.

The IPC values here are stable ground: Table 709.1 is value-identical from the 2015 through the 2024 editions, so the edition your jurisdiction adopted almost certainly matches this chart — but the amendment check is still yours to make. The UPC table shown is the 2021 edition, which added the nonwater drain-cleansing urinal row and the tub-to-shower retrofit allowance (note 9) over 2018. Two known state divergences are flagged directly on the rows: California and Hawaii omit hybrid urinals, and California amends the mobile-home trap value.