PEX Flow Rate Chart

Flow rate, water velocity and pressure loss per 100 feet for 3/8, 1/2, 3/4 and 1 inch PEX, transcribed from the manufacturer's published tables.

Read this before you use the chart

There is no single “max GPM” for a pipe size. A pipe carries as much water as you are willing to spend pressure on. Half-inch PEX will pass 5 GPM quite happily, it just costs you 32 psi for every 100 feet of it, which is most of a normal house’s supply pressure. Sizing is choosing how much pressure loss you can afford, then reading the flow off the table.

Pick an allowable loss for the run first. A common residential design target is a few psi per 100 feet in the trunk, then read across to the flow each size gives you at that number. Add the equivalent length of the fittings to the measured run before you do it, and remember elevation costs about 0.43 psi per foot of rise on top of friction.

These figures are for Uponor AquaPEX and Wirsbo hePEX specifically. All PEX to ASTM F876 shares the same outside diameters, but published inside diameters vary a little between manufacturers, and so does the flow at a given velocity. If you are installing another brand, check that brand’s own table before you rely on a borderline number.

3/8" PEX

Flow (GPM)	Velocity (ft/s)	Head loss, 60°F (ft per 100 ft)	Pressure loss, 60°F (psi per 100 ft)	Pressure loss, 140°F (psi per 100 ft)
0.5	1.67	3.07	1.33	1.13
1.0	3.33	13.77	5.96	5.07
1.5	5.00	31.19	13.50	11.48
2.0	6.67	54.87	23.75	20.19
2.5	8.34	84.54	36.60	31.11

1/2" PEX

Flow (GPM)	Velocity (ft/s)	Head loss, 60°F (ft per 100 ft)	Pressure loss, 60°F (psi per 100 ft)	Pressure loss, 140°F (psi per 100 ft)
0.5	0.91	1.05	0.45	0.39
1.0	1.81	3.79	1.64	1.39
1.5	2.72	8.02	3.47	2.95
2.0	3.62	13.65	5.91	5.03
2.5	4.53	20.63	8.93	7.59
3.0	5.43	28.91	12.52	10.64
3.5	6.34	38.45	16.65	14.15
4.0	7.24	49.22	21.31	18.11
4.5	8.15	61.21	26.50	22.52
5.0	9.05	74.38	32.20	27.37

3/4" PEX

Flow (GPM)	Velocity (ft/s)	Head loss, 60°F (ft per 100 ft)	Pressure loss, 60°F (psi per 100 ft)	Pressure loss, 140°F (psi per 100 ft)
1.0	0.91	0.71	0.31	0.26
1.5	1.36	1.49	0.65	0.55
2.0	1.81	2.54	1.10	0.94
2.5	2.27	3.84	1.66	1.42
3.0	2.72	5.38	2.33	1.98
4.0	3.63	9.17	3.97	3.37
5.0	4.54	13.85	6.00	5.10
6.0	5.44	19.41	8.40	7.14
7.0	6.35	25.81	11.17	9.50
8.0	7.26	33.05	14.31	12.16
9.0	8.17	41.09	17.79	15.12
10.0	9.07	49.93	21.61	18.37
11.0	9.98	59.56	25.78	21.92

1" PEX

Flow (GPM)	Velocity (ft/s)	Head loss, 60°F (ft per 100 ft)	Pressure loss, 60°F (psi per 100 ft)	Pressure loss, 140°F (psi per 100 ft)
2.0	1.10	0.75	0.32	0.28
3.0	1.65	1.59	0.69	0.58
4.0	2.20	2.71	1.17	1.00
5.0	2.75	4.09	1.77	1.51
6.0	3.30	5.74	2.48	2.11
8.0	4.40	9.77	4.23	3.59
10.0	5.50	14.76	6.39	5.43
12.0	6.60	20.68	8.95	7.61
14.0	7.70	27.51	11.91	10.12
16.0	8.80	35.22	15.25	12.96
18.0	9.90	43.79	18.96	16.11
20.0	11.00	53.21	23.03	19.58

Sources

Flow, velocity and head loss columns: Uponor, Pressure Loss Tables (document PressureLossTables_H191_1010), the 100% water tables for Wirsbo hePEX and Uponor AquaPEX. The gpm, velocity and “head (feet of water) per 100 feet of tubing” values at 60°F and 140°F are taken from that document unchanged.
psi columns: the published head in feet of water divided by 2.31 feet of water per psi. That conversion is the only arithmetic applied to any figure on this page.
Velocity limit: “Uponor recommends 12 ft./sec. maximum velocity for hot and cold domestic water systems using Uponor AquaPEX pipe and ProPEX fittings,” Uponor Commercial Plumbing Engineer Quick-reference Guide. Note that this is a manufacturer limit, not a design target: most residential systems run out of usable pressure long before they run out of velocity headroom, and local code may set a lower figure. The Canadian NPC, quoted in the same guide, defers to the manufacturer’s recommendation.
What is not on this page: fixture unit tables and fixture demand figures, because those are code tables that vary by jurisdiction and edition. Size the demand side from the code your inspector is enforcing, then use this chart for the pipe.

Working the chart

Measure the run, then add the fittings’ equivalent length. Every elbow and tee behaves like extra feet of pipe.
Decide the flow the run has to carry when the fixtures on it are used at the same time.
Read the psi per 100 ft for that flow in each candidate size, then scale it: a 40-foot run costs 0.4 of the table figure.
Add the elevation penalty, about 0.43 psi per foot of rise, and anything the water heater, softener, filter or manifold takes.
Compare the total against the pressure you actually have. If the remainder at the fixture is below what the fixture needs, go up a size and read again.

For the layout side of the decision, trunk-and-branch versus a manifold, and which size goes where, see the PEX plumbing sizing chart.

Additional Information

About this PEX flow rate chart

Most PEX flow charts online publish a single “maximum GPM” per pipe size with no pressure attached to it, and no source. That number cannot be right, because flow and pressure loss are the same fact seen from two sides. This page publishes the manufacturer’s own table instead: for each size, the velocity and the pressure it costs to move a given flow through 100 feet of tubing.

The 140°F column is there because hot water is genuinely cheaper to move. Water thins as it warms, so the same flow through the same pipe loses roughly 15 percent less pressure hot than cold. Sizing the hot side off cold-water figures is conservative, not wrong.

Every figure is checkable against the linked source document. If you find a transcription error, tell us and we will fix it, this is the kind of page where a wrong digit costs somebody a wall.

Frequently Asked Questions

What is the flow rate of 1/2" PEX?

There is no single answer, because the flow depends on how much pressure you are willing to lose. Uponor's published tables for 1/2" AquaPEX give 1 GPM at 1.81 ft/s costing 1.64 psi per 100 feet, 2 GPM at 3.62 ft/s costing 5.91 psi per 100 feet, 3 GPM at 5.43 ft/s costing 12.52 psi per 100 feet, and 5 GPM at 9.05 ft/s costing 32.20 psi per 100 feet. In a typical house with 50 psi at the meter, spending 32 psi on 100 feet of pipe is not a real option, which is why 1/2" is used for short drops to single fixtures rather than for distribution.

What is the flow rate of 3/4" PEX?

From the same Uponor tables: 3 GPM at 2.72 ft/s costs 2.33 psi per 100 feet, 5 GPM at 4.54 ft/s costs 6.00 psi per 100 feet, 8 GPM at 7.26 ft/s costs 14.31 psi per 100 feet, and 10 GPM at 9.07 ft/s costs 21.61 psi per 100 feet. Compare that with 1/2" at the same flow and you can see why 3/4" is the default for branches serving more than one fixture: at 3 GPM it costs about a fifth of the pressure.

How much pressure does PEX lose per 100 feet?

It depends entirely on size and flow. At 3 GPM and 60°F, Uponor publishes 12.52 psi per 100 feet for 1/2", 2.33 psi for 3/4" and 0.69 psi for 1". Going up one nominal size at a fixed flow cuts the loss several times over, three to five times in that example, which is the single most useful fact on this page. Scale linearly for shorter runs: a 25-foot run costs a quarter of the 100-foot figure.

Does hot water flow differently through PEX than cold?

Yes, and in the direction most people guess wrong. Warm water is less viscous, so it loses less pressure. Uponor's tables give 1/2" PEX at 2 GPM a loss of 5.91 psi per 100 feet at 60°F and 5.03 psi at 140°F, about 15 percent less. Sizing the hot side from cold-water numbers is therefore safe. What does change materially with temperature is the pipe's pressure rating, which falls as temperature rises, and that is a separate specification on the pipe print.

What is the maximum water velocity for PEX?

Uponor's Commercial Plumbing Engineer Quick-reference Guide states that "Uponor recommends 12 ft./sec. maximum velocity for hot and cold domestic water systems using Uponor AquaPEX pipe and ProPEX fittings." Other manufacturers publish different figures, and many designers work to a lower target for noise rather than damage. In practice velocity is rarely the binding constraint in a house: the pressure loss at 12 ft/s is severe enough that you will have sized up long before you get there.

How do I convert feet of head to psi?

Divide by 2.31. One psi lifts a column of water 2.31 feet, so 23.1 feet of head is 10 psi. Manufacturer pressure loss tables are often published in feet of head per 100 feet of pipe because that is the unit pump curves use, while domestic water pressure is talked about in psi. The psi columns on this page are the published head figures divided by 2.31, and nothing more.

Does the fitting type change the flow?

It changes the effective length, not the pipe. Insert fittings (the crimp and clamp systems used with PEX-B) neck the bore down at every joint and add more equivalent length than cold-expansion fittings, which keep the full inside diameter. On a long run with many joints that difference is worth accounting for. The tubing figures on this page are for the pipe itself; add the fittings as equivalent length before comparing against your available pressure.

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