Vent Pipe Size Chart — Stack Vents & Vent Stacks

How big the vent must be, and how far it may run: the IPC's full stack-vent and vent-stack matrix — maximum developed length by soil/waste stack size, DFU vented, and vent diameter — plus the UPC's per-size vent limits and the trap-to-vent distance table. IPC values per Table 906.1 (2021 edition; numbered 916.1 before 2015, values unchanged 2006–2024); UPC values per Table 703.2 (2021 edition). The two codes size vents differently — never mix their tables.

IPC — stack vents and vent stacks

IPC Table 906.1

Maximum developed length of the vent in feet — measured from the vent connection to open air — by soil or waste stack diameter, total DFU being vented, and vent diameter, values per IPC Table 906.1 (2021 edition). A dash means the code lists no value for that vent size; the diameter also may never be less than half the drain served, nor less than 1-1/4".
Stack	DFU vented	1-1/4" vent	1-1/2" vent	2" vent	2-1/2" vent	3" vent	4" vent	5" vent	6" vent	8" vent	10" vent	12" vent
1-1/4"	2	30	—	—	—	—	—	—	—	—	—	—
1-1/2"	8	50	150	—	—	—	—	—	—	—	—	—
1-1/2"	10	30	100	—	—	—	—	—	—	—	—	—
2"	12	30	75	200	—	—	—	—	—	—	—	—
2"	20	26	50	150	—	—	—	—	—	—	—	—
2-1/2"	42	—	30	100	300	—	—	—	—	—	—	—
3"	10	—	42	150	360	1,040	—	—	—	—	—	—
3"	21	—	32	110	270	810	—	—	—	—	—	—
3"	53	—	27	94	230	680	—	—	—	—	—	—
3"	102	—	25	86	210	620	—	—	—	—	—	—
4"	43	—	—	35	85	250	980	—	—	—	—	—
4"	140	—	—	27	65	200	750	—	—	—	—	—
4"	320	—	—	23	55	170	640	—	—	—	—	—
4"	540	—	—	21	50	150	580	—	—	—	—	—
5"	190	—	—	—	28	82	320	990	—	—	—	—
5"	490	—	—	—	21	63	250	760	—	—	—	—
5"	940	—	—	—	18	53	210	670	—	—	—	—
5"	1,400	—	—	—	16	49	190	590	—	—	—	—
6"	500	—	—	—	—	33	130	400	1,000	—	—	—
6"	1,100	—	—	—	—	26	100	310	780	—	—	—
6"	2,000	—	—	—	—	22	84	260	660	—	—	—
6"	2,900	—	—	—	—	20	77	240	600	—	—	—
8"	1,800	—	—	—	—	—	31	95	240	940	—	—
8"	3,400 †	—	—	—	—	—	24	73	190	729	—	—
8"	5,600	—	—	—	—	—	20	62	160	610	—	—
8"	7,600	—	—	—	—	—	18	56	140	560	—	—
10"	4,000	—	—	—	—	—	—	31	78	310	960	—
10"	7,200	—	—	—	—	—	—	24	60	240	740	—
10"	11,000	—	—	—	—	—	—	20	51	200	630	—
10"	15,000 ‡	—	—	—	—	—	—	18	46	180	see ‡	—
12"	7,300	—	—	—	—	—	—	—	31	120	380	940
12"	13,000	—	—	—	—	—	—	—	24	94	300	720
12"	20,000	—	—	—	—	—	—	—	20	79	250	610
12"	26,000	—	—	—	—	—	—	—	18	72	230	500
15"	15,000	—	—	—	—	—	—	—	—	40	130	310
15"	25,000	—	—	—	—	—	—	—	—	31	96	240
15"	38,000	—	—	—	—	—	—	—	—	26	81	200
15"	50,000	—	—	—	—	—	—	—	—	24	74	180

† The 2021 print reads 729 feet here (two independent 2021 witnesses); editions before the 2015 re-typeset print 720. Cited per the 2021 text.
‡ Editions before 2015 print 570 feet here; the 2021 re-typeset value could not be independently double-confirmed (one transcription family shows 571). Omitted rather than guessed — read this one cell from the enforced code book.

IPC — distance of trap from vent

IPC Table 909.1

Maximum distance from the trap weir to the vent fitting, by trap size at the fixture drain's slope, values per IPC Table 909.1 (2021 edition).
Trap size	Drain slope	Max distance
1-1/4"	1/4" per ft	5 ft
1-1/2"	1/4" per ft	6 ft
2"	1/4" per ft	8 ft
3"	1/8" per ft	12 ft
4"	1/8" per ft	16 ft

Self-siphoning fixtures such as water closets are not limited in trap-to-vent distance. The total fall of a fixture drain may not exceed one pipe diameter, and (water closets excepted) the vent connection may not sit below the weir of the trap.

UPC — vent capacity and length limits

UPC Table 703.2

Maximum fixture units and maximum developed length per vent size, values per the vent rows of UPC Table 703.2 (2021 edition). The code tabulates no limits for 10" and 12" vents, and the 2015+ UPC has no 2-1/2" size.
Vent size	Max fixture units	Max length	Notes
1-1/4"	1	45 ft	—
1-1/2"	8	60 ft	3
2"	24	120 ft	—
3"	84	212 ft	—
4"	256	300 ft	—
5"	600	390 ft	—
6"	1,380	510 ft	—
8"	3,600	750 ft	—
10"	—	—	—
12"	—	—	—

3 — No water closets or six-unit traps on this size. Individual vents: An individual vent is never smaller than 1-1/4" nor smaller than half the diameter of the drain it serves. Not more than one-third of a vent's permitted length may run horizontal — unless the vent is increased one pipe size for its entire length, which removes the length limit entirely.

How the two codes size a vent

Under the IPC, a stack vent or vent stack reads the big matrix: find your stack size, drop to the row covering the DFU actually vented, and read across for the smallest vent diameter whose developed length covers your run. Individual, branch, circuit, and relief vents are at least half the required diameter of the drain served (drain size per Table 710.1(2)), never smaller than 1-1/4". A vent running over 40 feet of developed length steps up one nominal size for its entire length. Developed length of individual/branch/circuit/relief vents is measured from the farthest vent connection to the drainage system to the vent stack, stack vent, or open-air termination. Total the DFU with the DFU chart or the fixture unit calculator.

The UPC works per size: each vent diameter carries a fixture-unit cap and a length cap straight from Table 703.2. Vent piping sizes from its length and connected fixture units per Table 703.2 — and the building's vents must together provide an aggregate cross-sectional area at least equal to the largest required building sewer. Vents from fixtures upstream of pumps, ejectors, or backwater valves don't count toward that aggregate. The one-third-horizontal rule (Section 904.2) is the working constraint crews hit most: no more than a third of the permitted length may lie horizontal — unless the whole vent is upsized one pipe size, which lifts the length limit entirely.

Two cells, two editions — read the fine print

This table has been numerically stable since at least 2006, with two exceptions introduced by the 2015 re-typeset, both on the largest stacks: the 8" stack / 3,400 DFU row prints 729 feet on an 8" vent in current editions where older editions print 720, and the 10" stack / 15,000 DFU row's 10" cell could not be independently double-confirmed in the current print, so this chart omits that one cell rather than guess. Both are footnoted above. If your jurisdiction enforces a pre-2015 edition, the section number changes too — Table 916.1 rather than 906.1 — and local amendments can rewrite any of it (Chicago replaces the entire vent table). Confirm the enforced code, edition, and amendments.

Common questions

What size vent does a toilet need?

Both codes size an individual vent at no less than half the diameter of the drain it serves, and never smaller than 1-1/4". A water closet on a 3" drain therefore takes a 1-1/2" individual vent minimum — IPC 906.2 and the UPC's Table 703.2 note agree on the rule, though each code's stack tables differ beyond that.

How long can a vent pipe run?

Under the IPC, stack vents and vent stacks read their maximum developed length from Table 906.1 — a 4" stack venting 540 DFU allows a 3" vent up to 150 feet or a 4" vent to 580 feet — while individual and branch vents have no absolute cap but must upsize one pipe size once they exceed 40 feet. The UPC caps each vent size directly: 120 feet on 2", 300 feet on 4" — and removes the cap entirely if you upsize the whole vent by one size.

How far can a trap be from the vent?

Under IPC Table 909.1: 5 feet for a 1-1/4" trap, 6 feet for 1-1/2", 8 feet for 2" (all at 1/4" per foot), 12 feet for 3" and 16 feet for 4" (at 1/8" per foot). Self-siphoning fixtures like water closets are exempt from the distance limit. The UPC handles trap-arm limits in its own Chapter 10 — don't carry these values across.

Is IPC Table 916.1 the same as Table 906.1?

Same table, renumbered. The IPC reorganized Chapter 9 in the 2015 edition: vent pipe sizing moved from Section 916 to Section 906, and Section 916 now covers island fixture venting. The values themselves have been stable since at least 2006 — if your jurisdiction enforces a pre-2015 edition, cite 916.1; from 2015 on, cite 906.1.

RUN THE NUMBERS

Run your whole job on the same numbers

These NORDIX tools are a taste of the full platform — bid pipeline, estimating, and job costing that carry your numbers from the first bid to the final invoice.

See what NORDIX does →