Water Flow Chart #1 The chart below takes into consideration the potential damage from hydraulic hammer (shock) and noise considerations due to excessive fluid velocity. For more detailed information click here for our pipe selection based on pipe size and flow requirement Nomograph. You can flow more than what is shown in the chart (see Chart #2 below) however, you may run into problems if you do.
IMPORTANT: The flow ratings in the charts below are for Rigid PVC Pipe. Reduce flow by 3% (Multiply by .97) for flow going through Flexible PVC Pipe.



Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump 
Assume Average Pressure. (20100PSI) About 12f/s flow velocity 
Assume "High Pressure" PEAK flow. About 18f/s flow velocity^{*} 
Sch 40 Pipe Size 
ID
(range) 
OD 
GPM
(with minimal pressure loss & noise) 
GPH
(with minimal pressure loss & noise) 
GPM
(with minimal pressure loss & noise) 
GPH
(with minimal pressure loss & noise) 
GPM
(with significant pressure loss & noise) 
GPH
(with significant pressure loss & noise) 
1/2" 
.50.60" 
.85" 
7 gpm 
420 gph 
14 gpm 
840 gph 
21 gpm 
1,260 gph 
3/4" 
.75.85" 
1.06" 
11 gpm 
660 gph 
23 gpm 
1,410 gph 
36 gpm 
2,160 gph 
1" 
1.001.03" 
1.33" 
16 gpm 
960 gph 
37 gpm 
2,220 gph 
58 gpm 
3,510 gph 
1.25" 
1.251.36" 
1.67" 
25 gpm 
1,500 gph 
62 gpm 
3,750 gph 
100 gpm 
5,940 gph 
1.5" 
1.501.60" 
1.90" 
35 gpm 
2100 gph 
81 gpm 
4,830 gph 
126 gpm 
7,560 gph 
2" 
1.952.05" 
2.38" 
55 gpm 
3300 gph 
127 gpm 
7,650 gph 
200 gpm 
12,000 gph 
2.5" 
2.352.45" 
2.89" 
80 gpm 
4800 gph 
190 gpm 
11,400 gph 
300 gpm 
17,550 gph 
3" 
2.903.05" 
3.50" 
140 gpm 
8400 gph 
273 gpm 
16,350 gph 
425 gpm 
25,650 gph 
4" 
3.853.95" 
4.50" 
240 gpm 
14,400 gph 
480 gpm 
28,800 gph 
700 gpm 
42,000 gph 
5" 
4.955.05" 
5.563" 
380 gpm 
22,800 gph 
750 gpm 
45,000 gph 
1100 gpm 
66,000 gph 
6" 
5.855.95" 
6.61" 
550 gpm 
33,000 gph 
1100 gpm 
66,000 gph 
1700 gpm 
102,000 gph 
8" 
7.96" 
8.625" 
950 gpm 
57,000 gph 
1900 gpm 
114,000 gph 
2800 gpm 
168,000 gph 
Water Flow Chart #2
Here is a set of data predicting the amount of flow through an orifice based on pressure on one side of the orifice. Note: This is through an orifice, not a pipe. Adding pipe and fittings will drop this flow significantly. In other words, this would be the theoretical maximum amount of water through a hole based on the pressure above it. The table above is more "real world" information.
Pressure 
Flow in GPM through a hole diameter measured in inches 
PSI 
1" 
1.25" 
1.5" 
2" 
2.5" 
3" 
4" 
5" 
20 
26 
47 
76 
161 
290 
468 
997 
2895 
30 
32 
58 
94 
200 
360 
582 
1240 
3603 
40 
38 
68 
110 
234 
421 
680 
1449 
4209 
50 
43 
77 
124 
264 
475 
767 
1635 
4748 
60 
47 
85 
137 
291 
524 
846 
1804 
5239 
75 
53 
95 
153 
329 
591 
955 
2035 
5910 
100 
62 
112 
180 
384 
690 
1115 
2377 
6904 
125 
70 
126 
203 
433 
779 
1258 
2681 
7788 
150 
77 
139 
224 
478 
859 
1388 
2958 
8593 
200 
90 
162 
262 
558 
1004 
1621 
3455 
10038 
Water Flow Chart #3
This chart predicts how much flow you will get across a stainless metal ball valve of the diameter & length specified with a 1PSI pressure drop from one side of the valve assuming about 100psi on one side of the valve.
Size (ID, inches) 
Length (inches) 
Flow (GPM) 
1/2 
4.25 
26 
3/4 
4.62 
50 
1 
5.00 
94 
11/2 
6.50 
260 
2 
7.00 
480 
21/2 
7.50 
750 
3 
8.00 
1300 
4 
9.00 
2300 
6 
15.50 
5400 
Note: The data is for water through the valve only, and does not take into account the rest of the system. It does not give flow velocity, so there is some question as to the applicability of the data. The data
comes from a book for industrial piping and probably assumes a massive pump, high flow velocities and metallic pipes. (Ie, where water hammer and noise are less of a concern than with PVC pipe.) As always, "you mileage may vary."


GPM/GPH Flow based on PVC Pipe Size
There are now 3 charts and one formula on this page showing water flow through a pipe. These 3 charts come from 3 different sources, and they all are just general guidelines. and should not be relied on as a
precise source for information or as a substitute for engineering. The data between them does vary. In the chart to the left is a general guideline for how much liquid a pipe of specific size can flow in GPM (Gallons Per Minute) & GPH
(Gallons Per Hour.) There are three columns. (Well there are really six, but each colum is shown in Gallons per minute, and then again as Gallons per Hour.) The first set of columns would be the minimum you would expect for the pipe size
shown using nothing but gravity in a low head pressure situation to power the flow. The 2nd set of columns show what you can expect using an average pump with a pressure from 20 to 100psi. The 3rd set of columns is the maximum flow based
on maximum recommended velocity of the liquid in the pipe. You may exceed this, but you will have to contend with excessive noise and exceedingly high inertial impacts. (I.e. Possible system failure due to hydraulic hammer effects.) This
is a very general guide and is subject to many variables. Pressure, noise allowance, bends, fittings, viscosity, etc. affect how much liquid will flow through a pipe of given size. If you can accept more noise and have higher pressure, you
can pump more at the risk of system failure. If you have a lot of bends and fittings you will flow less. The flow rates shown should not produce unacceptable noise, however, many variables affect noise, so this is no guarantee that the
system will be noiseless. Sometimes experimentation is the only sure way to know if a system will be noisy or not. The flow rates shown are for water, with viscosity of 1. Higher viscosity liquids will flow less, lower viscosity liquids
may flow more. You can use the HazenWilliams equation below to calculate the exact flow loss through a pipe.
Pipe Size vs Flow Nomograph
The nomograph (link above) allows you visually see the effect of pipe size and flow rates. You can click on the link and print it out to make it more usable to you. You should size your pipe so that your flow velocity stays in the green
or yellow range. The green range is safest, most efficient and will produce little to no noise. Flow velocities in the yellow range may be noisy and have additional back pressure. Flow velocities in the red are not recommended because of
the risk of hydraulic shock and pipe/fitting/joint & pump failure.
Note: Back pressure (restriction) is exponentially dependent on flow velocity. For example in a 1" pipe going from a flow velocity of 2 ft/sect (about 5gpm) to a flow velocity of 3.86 ft/sec (about 10gpm) will increase back pressure by
300%. Going to a flow velocity of 7.71ft/sec (about 20gpm) will increase back pressure by 1300%!
These figures are for straight pipe only! The effect of putting direction changes in will compound the back pressure even more and could even result in failure of the system or burning up the pump. You will never be hurt by going to a
bigger pipe and will gain by using less electricity due to a more efficient system which may offset the initial price difference for the larger pipe.
Find your flow in the first column (GPM) and then select the pipe size you want in the second column (pipe, ID in inches.) Draw a straight line between them all the way to the last column. If the line ends up in the green you are good.
If it ends in the yellow or red, increase the pipe size until your line ends in the green (best) or yellow (just okay) area.
Friction Loss Further Detailed Information
If you really want to get technical and calculate the exact friction loss through PVC and CPVC pipe you can use the HazenWilliams equation as expressed below for water:
f = 0.2083 (100/c)^{1.852} q^{1.852} / d_{h}^{4.8655}
where
f = friction head loss in feet of water per 100 feet of pipe (ft_{h20}/100 ft pipe)
q = volume flow (gal/min)
d_{h} = inside diameter (inches)
c = a constant for internal pipe roughness. 150 is the commonly accepted value for PVC and CPVC pipe.
You can also print out and use the Nomograph courtesy of Plastics Pipe Institute, a division of The Society of The Plastics Industry. (Note: You normally want to keep your flow velocity under 12 feet per second for 4" and under and 5 feet/second for 5" and above to avoid hydraulic shock.)
What about fittings? How do they affect flow? See our Friction loss due to pvc pipe fittings chart.
Compared to other materials on construction for pipe, thermoplastic pipe smoothness remains relatively constant throughout its service life.
If you are flowing something other than water, you'll have to adjust the formula for the viscosity of the liquid you are flowing.
Note: One of the benefits of using Flexible PVC pipe is being able to make long gradual bends instead of using fittings which will allow more flow with less noise, less back pressure, and less load on the pump. In other words, a more efficient system!
^{*}"High Pressure" is a general and nonspecific figure. What might be "high pressure" for 1/2" pipe (600psi) may not be "high pressure" for 2" pipe (280psi). There are just too many variables to consider to
give a real world number. The fact of the matter is, on a pressurized system, the pump will dictate the flow and pressure as much as the pipe used. To achieve the flow figures in the peak column, it's assuming there are no bends and a
short straight flow path. If your system has bends and T's, Wyes, etc, you should go to a larger pipe to achieve the flow desired. Also feed pressure effects the system. If the feed pressure is too low, you can get cavitation and you'll
damage the pump and flow very little.
