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Fire Hose Friction Loss Formula

Friction Loss occurs when water is pumped through a hose or pipe.  Distance, diameter, and the GPM all affect friction loss.  As water passes through the fire hose, friction develops between the moving water and the inside surface of the hose.  This turbulance reduces the PSI at the other end of the hose.  The friction loss formula calculates the friction loss for hoses between 3/4" & 6" diameter.

Use the following formula to determine friction loss.  You can use a scientific calculator or if you are good with math, write out the equation by hand to solve for friction loss.  Create your own friction loss problems, like the problem below, and solve for the answer.  Use the online Friction Loss Calculator to verify your answer.



Fire Hose Friction Loss Formula

FL = C * (Q / 100) ^2 * L / 100

FL = Friction loss in PSI
C = Friction loss Coefficient (Table 1)
Q = Flow rate in GPM
L = Hose length


Example:
Determine the friction loss for a 100 foot section of 1 inch hose with 60 GPM of flow.

FL = C * (Q / 100) ^2 * L / 100
54.0 = 150 * (60 / 100) ^2 * 100 / 100


Coefficient (C) for 1" hose is 150
GPM (Q) = 60 GPM
Length (L) = 100 feet

Answer: There is 54.0 PSI of friction loss for a 100 foot section of 1 inch hose with 60 GPM of water passing through it.
Table 1

Friction Loss Coefficient

Diameter Coefficient
0.75 inch hose 1100
1  inch hose 150
1 ¼   inch hose 80
1 ½  inch hose 24
1 ¾  inch hose 15.5
2 inch hose 8
2 ½ inch hose 2
3 inch hose 0.677
3 ½ inch hose 0.34
4  inch hose 0.2
4 ½ inch hose 0.1
5 inch hose 0.08
6 inch hose 0.05

Methods to determining friction loss calculations:

  • The Friction Loss Formula calculates friction loss for fire hose between 3/4" & 6" and is the most accurate method.  But, determining friction loss with this method is the most time intensive, has a high probablity for human error, and is not very practical in the field or for learning hydraulics theory. 
  • The Friction Loss Calculator will calculate Friction loss for any size fire hose between 3/4" & 6".  This method uses the friction loss formula to perform calculations and is just as accurate.
  • The Friction Loss Slide Rule can provide calculations for a wide variety of hose sizes and is faster than the friction loss formula, but it has a higher probability for human error, and the slide rule is the least accurate of the three methods.
  • The Friction Loss Chart (by FireDepartment.net) provides a friction loss chart for each size of hose between 3/4" & 6".  The Friction Loss Grid is a little more bulky, but is the easiest, fastest, and a very accurate method of determining friction loss. 
  • Information about Hardware Friction Loss.

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