What size water line do I need for my house?

Under IPC Appendix E, it depends on fixture units, pressure and length. Two bathroom groups, a kitchen sink, dishwasher and washer total 11.4 wsfu; at 55 psi and 100 feet of pipe that is a 3/4 inch service and meter with a 1 inch main. At 35 psi the same house needs a 1 inch meter. The minimum building supply is 3/4 inch.

How many fixture units is a bathroom for water supply?

A private bathroom group with a flush tank toilet is 3.6 water supply fixture units combined, 2.7 cold and 1.5 hot, in IPC Table E103.3(2). A kitchen sink, dishwasher, clothes washer, bathtub or shower is 1.4 each and a lavatory 0.7.

How much pressure do I lose per floor?

IPC Appendix E uses two figures: 0.5 psi per foot of height in the E201.1 sizing steps and 0.433 psi per foot in Section E103.2.2. 0.433 is the weight of a foot of water. A 10 foot storey costs 4.3 to 5 psi.

What is the inside diameter of 1/2 inch PEX?

Uponor's AquaPEX submittal gives 0.475 inch, and the internal volume in IPC Table E202.1 converts to the same figure. 3/4 inch PEX is 0.671 inch and 1 inch 0.862 to 0.865.

Is there an error in the IPC water pipe sizing tables?

Table E103.3(3) prints six cubic feet per minute values that do not match the gallons beside them, the first two about a tenth of the right figure, in the San Antonio, Phoenix, Michigan and New York City adoptions. Table E201.1 lists 365 fixture units at 40 feet and 368 at 60 feet on one row. The gallons columns the sizing uses are consistent.

Do I need a pressure reducing valve?

IPC Section 604.8 requires one where static pressure in the building exceeds 80 psi, set to no more than 80 psi. For sizing, Appendix E then uses 80 per cent of the street pressure or the valve setting, whichever is smaller.

Does Appendix E apply where I live?

Only where the jurisdiction adopts it; it is an appendix to the IPC, not part of the code by default. States on the Uniform Plumbing Code use their own sizing tables.

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Water Pipe Size Calculator

IPC Appendix E sizing, and the tables in it that disagree with each other

The plumbing code's water sizing appendix is a five step procedure, and read cell by cell it disagrees with itself. Its demand table converts gallons to cubic feet wrongly in six places, identically in four jurisdictions. Its sizing table gains capacity with distance on one row. It deducts 0.5 psi a foot for height in one section and 0.433 in another. And the main code's manifold table assumes a pipe bore equal to its nominal size, which the appendix's own volume table shows no PEX or copper has.

Water service, meter and main by IPC Appendix E

Bathroom groups (flush tank, 3.6 wsfu)

no.

Kitchen sinks

no.

Dishwashers

no.

Clothes washers

no.

Laundry trays

no.

Extra lavatories

no.

Extra bathtubs

no.

Extra showers

no.

Minimum static pressure

psi

Highest outlet above the meter

Pressure-reducing valve set pressure (0 if none)

psi

Equipment losses (softener, filter, backflow)

psi

Fixture needing 20 psi (thermostatic shower, flushometer tank)

Pipe run to the most remote fixture

Pipe material, for velocity

Use the minimum daily static pressure from your water utility, not a gauge reading at a quiet hour. Developed length is the pipe run from the meter to the most remote fixture, hot or cold; the calculator adds the appendix's 20 per cent for fittings.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

Velocity in the main distribution pipe

Worked example

A house with two bathroom groups, a kitchen sink, a dishwasher and a clothes washer, 55 psi at the meter, 100 feet of pipe to the farthest fixture, plumbed in PEX.

Fixture units. 2 × 3.6 + 1.4 + 1.4 + 1.4 = 11.4 wsfu.
Pressure. 55 psi with no height, valve or equipment: the 50 to 60 psi band.
Length. 100 × 1.2 = 120 ft, so the 150 ft column.
Read down. 3/4 in meter with 1/2 in main carries 1.5; with 3/4 in, 6.5; with 1 in, 25. First to reach 11.4: 3/4 in service and meter, 1 in main.
Velocity. Table E103.3(3) puts 11.4 wsfu at 16.0 gpm. Through the 0.865 in bore of 1 in PEX that is 8.7 ft/s.
With 20 ft of height at 45 psi. 45 − 20 × 0.5 = 35 psi, the 30 to 39 band: 1 in service and meter, 1 in main.

The same house goes up a meter size for twenty feet of height. At 0.433 psi a foot, the other figure in the same appendix, it would have 36.3 psi, still in the same band; the difference matters only near a band edge.

The formula

Appendix E's steps, in order:

available psi = static − 0.5 × height − equipment − (fixture psi − 8) developed length = run × 1.2 velocity (ft/s) = gpm ÷ (2.448 × bore²)

wsfu: water supply fixture units, Table E103.3(2), combined column for the service and main
pressure-reducing valve: available pressure is 80 per cent of static or the valve's set pressure, whichever is smaller
1.2: the appendix's allowance for fittings on the developed length
bore: inside diameter from the ounces per foot in Table E202.1
2.448: gallons per minute per foot per second through a one inch bore

Table E201.1 is read down the length column to the first row whose capacity reaches the load, in the order printed. The meter and service size is the first column of that row, the main distribution pipe the second.

Why this page checks the appendix before using it

Pipe sizing calculators pick a size from a rule of thumb or a velocity. The code's own method is an appendix of tables that most pages never reproduce.

Reproducing them meant reading every cell. The cubic feet column of the demand table fails to convert in six places, the sizing table rises with length once, the appendix prices height two ways, and the main code's manifold table assumes a bore that the appendix's volume table contradicts.

None of this changes a typical house's answer much. It does show which numbers in the tables were computed and which were typed.

Manifold flow at 8 ft/s against real pipe bores
Nominal	Table 604.10.1 at 8 ft/s	PEX bore from E202.1	Uponor's printed bore	Real velocity in PEX	Type L copper bore	Real velocity in Type L
1/2 in	5 gpm	0.475 in	0.475 in	9.0 ft/s	0.545 in	6.9 ft/s
3/4 in	11 gpm	0.671 in	0.671 in	10.0 ft/s	0.785 in	7.3 ft/s
1 in	20 gpm	0.865 in	0.862 in	10.9 ft/s	1.025 in	7.8 ft/s
1 1/4 in	31 gpm	1.055 in	—	11.4 ft/s	1.265 in	7.9 ft/s
1 1/2 in	44 gpm	1.245 in	—	11.6 ft/s	1.505 in	7.9 ft/s

Read 2026-09-13. Table 604.10.1 from Texas IPC 2021; bores computed from Table E202.1 in San Antonio's IPC 2018 Appendix E; Uponor submittal for comparison.

Download this table as CSV. Same cells as printed above, nothing added.

The code's water sizing appendix, checked against itself

Appendix E sizes the water service and main distribution pipe in five steps: fixture units, available pressure, developed length, then a table read down one column to the first row that carries the load. It is published as an appendix, so it applies where a jurisdiction adopts it; San Antonio and Phoenix are two that do.

Its demand table converts gallons to cubic feet wrongly in six places. Table E103.3(3) prints both units, and a gallon a minute is 0.13368 cubic feet a minute. Every figure matches except these:

Table E103.3(3), printed cubic feet per minute against the gallons printed beside them
Column	Load, wsfu	Demand, gpm	Printed cfm	gpm × 0.13368
flush tank	1	3	0.04104	0.40104
flush tank	2	5	0.0684	0.6684
flushometer	7	19.8	2.64636	2.64686
flush tank	16	18	2.90624	2.40624
flushometer	16	31.8	4.24102	4.25102
flushometer	30	42	5.61356	5.61456

The first two are about a tenth of the right figure. The same six cells are printed in the San Antonio and Phoenix 2018 adoptions, Michigan's 2015 code and New York City's 2022 code. Four jurisdictions and three editions sharing identical slips means they copied them; the model code's own text could not be read to confirm.

Its sizing table gains capacity with distance once. In the over 60 psi band, a 2 inch meter with a 2 inch main carries 365 fixture units at 40 feet and 368 at 60 feet. Friction only grows with length; everywhere else in Table E201.1 the numbers fall or hold.

And it prices a foot of height two ways. Step 2.1 of E201.1:

Where the highest water supply outlet is located above the source of supply, deduct 0.5 psi (3.4 kPa) for each foot (0.3 m) of difference in elevation.

Section E103.2.2, in the same appendix:

Static pressure loss or gain (due to head) is computed at 0.433 psi per foot (9.8 kPa/m) of elevation change.

0.433 is the weight of a foot of water. 0.5 rounds it up by 15 per cent, which errs safe. The calculator uses 0.5 because that is the step the sizing table belongs to, and shows the difference.

The manifold table's pipe does not exist

Table 604.10.1 sizes PEX and copper manifolds by flow at 4 and 8 feet per second. Its heading calls the first column nominal size internal diameter, and every cell is exactly the flow at that velocity through a bore equal to the nominal size: 1/2 inch at 8 feet per second is 4.9 gallons a minute, printed as 5.

Nominal size is not bore. Appendix E's own Table E202.1 lists the water held in a foot of each pipe, and that converts to the inside diameter. For PEX it gives exactly what Uponor prints on its submittal. For Type L copper the bore is larger than nominal.

Flow at the table's 8 ft/s, through the real bores the same code publishes
Nominal	Table 604.10.1 at 8 ft/s	PEX bore from E202.1	Uponor's printed bore	Real velocity in PEX	Type L copper bore	Real velocity in Type L
1/2 in	5 gpm	0.475 in	0.475 in	9.0 ft/s	0.545 in	6.9 ft/s
3/4 in	11 gpm	0.671 in	0.671 in	10.0 ft/s	0.785 in	7.3 ft/s
1 in	20 gpm	0.865 in	0.862 in	10.9 ft/s	1.025 in	7.8 ft/s
1 1/4 in	31 gpm	1.055 in	—	11.4 ft/s	1.265 in	7.9 ft/s
1 1/2 in	44 gpm	1.245 in	—	11.6 ft/s	1.505 in	7.9 ft/s

Sized by the table, PEX manifolds and branches run 13 to 45 per cent faster than the velocity the table names, and copper slower. Section 604.9 asks for velocity to be controlled to reduce water hammer; the table meant to do that assumes a bore that neither material has.

What the code sets outside the appendix

Fixtures need flow and pressure at the outlet. Table 604.3 sets, for example, 2.5 gpm at 8 psi for a shower, 1.75 gpm for a residential sink and 0.8 gpm for a private lavatory, and 20 psi for a thermostatic or pressure-balancing shower valve.

Fixture supplies have minimum sizes. Table 604.5 sets 3/8 inch for a lavatory or a tank toilet and 1/2 inch for a kitchen sink, dishwasher, shower, bathtub or hose bibb, with the supply ending within 30 inches of the fixture.

Pressure above 80 psi needs a reducing valve. Section 604.8 requires one to bring building distribution down to 80 psi static.

The sources, and the editions

Read 2026-09-13.

San Antonio Plumbing Code 2018, Appendix E Sizing of Water Piping System, International Plumbing Code 2018 as adopted with amendments in San Antonio, read through UpCodes with the jurisdiction and edition stated on the page. Sections E101 to E202, Tables E103.3(2), E103.3(3), E201.1 and E202.1. The Phoenix 2018 adoption prints the same tables identically.

Texas IHB Plumbing Code 2021, Chapter 6 Water Supply and Distribution, International Plumbing Code 2021 as adopted with amendments in Texas, read through UpCodes with the jurisdiction and edition stated on the page. Sections 604.3 to 604.10 and Tables 604.3, 604.4, 604.5 and 604.10.1.

Appendix E as adopted in Phoenix 2018, Michigan 2015 and New York City 2022, Read through UpCodes to compare Table E103.3(3) across adoptions. All four adoptions print the same six cubic feet per minute figures that do not convert.

Uponor AquaPEX white coils submittal, Uponor, manufacturer's submittal sheet. Inner and outer diameter of pipe by size.

Two editions are mixed deliberately. Appendix E is read from San Antonio's 2018 adoption because Texas's 2021 text on UpCodes does not include it; Chapter 6 is read from the 2021 Texas adoption. The appendix applies only where it is adopted. States on the Uniform Plumbing Code size water pipe from their own tables.

A footnote in the fixture unit table contradicts its own rows. It says hot and cold loads are three-fourths of the total in each case, but a flush tank bathroom group is printed at 2.7 cold, 1.5 hot and 3.6 total, because the toilet takes no hot water. The rows are right and the footnote is not.

Frequently asked questions

What size water line do I need for my house?: Under IPC Appendix E, it depends on fixture units, pressure and length. Two bathroom groups, a kitchen sink, dishwasher and washer total 11.4 wsfu; at 55 psi and 100 feet of pipe that is a 3/4 inch service and meter with a 1 inch main. At 35 psi the same house needs a 1 inch meter. The minimum building supply is 3/4 inch.
How many fixture units is a bathroom for water supply?: A private bathroom group with a flush tank toilet is 3.6 water supply fixture units combined, 2.7 cold and 1.5 hot, in IPC Table E103.3(2). A kitchen sink, dishwasher, clothes washer, bathtub or shower is 1.4 each and a lavatory 0.7.
How much pressure do I lose per floor?: IPC Appendix E uses two figures: 0.5 psi per foot of height in the E201.1 sizing steps and 0.433 psi per foot in Section E103.2.2. 0.433 is the weight of a foot of water. A 10 foot storey costs 4.3 to 5 psi.
What is the inside diameter of 1/2 inch PEX?: Uponor's AquaPEX submittal gives 0.475 inch, and the internal volume in IPC Table E202.1 converts to the same figure. 3/4 inch PEX is 0.671 inch and 1 inch 0.862 to 0.865.
How fast should water flow in a pipe?: IPC Table 604.10.1 sizes manifolds for 4 and 8 feet per second, and Section 604.9 asks for velocity to be controlled to reduce water hammer. The table's flows assume a bore equal to nominal size; in PEX the same flows run 13 to 45 per cent faster.
Is there an error in the IPC water pipe sizing tables?: Table E103.3(3) prints six cubic feet per minute values that do not match the gallons beside them, the first two about a tenth of the right figure, in the San Antonio, Phoenix, Michigan and New York City adoptions. Table E201.1 lists 365 fixture units at 40 feet and 368 at 60 feet on one row. The gallons columns the sizing uses are consistent.
Do I need a pressure reducing valve?: IPC Section 604.8 requires one where static pressure in the building exceeds 80 psi, set to no more than 80 psi. For sizing, Appendix E then uses 80 per cent of the street pressure or the valve setting, whichever is smaller.
Does Appendix E apply where I live?: Only where the jurisdiction adopts it; it is an appendix to the IPC, not part of the code by default. States on the Uniform Plumbing Code use their own sizing tables.

Check these numbers yourself

San Antonio Plumbing Code 2018, Appendix EIPC 2018 as adopted in San Antonio, read 2026-09-13 through UpCodes with the jurisdiction and edition stated on the page. Tables E103.3(2), E103.3(3), E201.1 and E202.1; Phoenix 2018 identical.
Texas IHB Plumbing Code 2021, Chapter 6IPC 2021 as adopted in Texas, read 2026-09-13. Sections 604.3 to 604.10.
New York City Plumbing Code 2022, Appendix ERead 2026-09-13 with the Phoenix 2018 and Michigan 2015 adoptions to compare Table E103.3(3).
Uponor AquaPEX white coils submittalUponor, read 2026-09-13. Inner diameter of pipe by size.

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-13. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

The sizing follows IPC Appendix E as adopted in San Antonio in 2018, read on 13 September 2026, and applies only where a jurisdiction adopts that appendix. It sizes the water service, meter and main distribution pipe, not individual branches. Water service work commonly needs a permit and the utility sets meter sizes. This site publishes no price of its own.