Friction Loss Formula

Learn how to solve fire hose friction loss with the friction loss formula. Below, you'll find the formula and an example of solving the friction loss formula. We also provided friction loss problems for you to solve, alonw with a link to the answer of each problem. You can also create your own problems and check your answers with the Friction Loss Calculator

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

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


Example:

What is the friction loss for a 200 foot of 1.75 inch fire hose flowing 150 GPM of water?

Coefficient (C) for 1.75" hose is 15.5 (See Table)
GPM (Q) = 150 GPM
Length (L) = 200 feet

FL = C * (Q / 100) ^2 * L / 100
69.75 = 15.5 * (150 / 100)^2 * 200 / 100

Answer: There's 69.75 PSI friction loss for a 200 foot of 1.75 inch hose with 150 GPM.

Answer verified in the friction loss calculator

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

Practice solving friction loss equations and check your answer with the link:

What is the friction loss of 200 feet of 1.75" hose with 200 gpm? Answer 200' of 1.75" hose flowing 200 GPM

What is the friction loss of 150 feet of 2" hose with 500 gpm? Answer 150' of 2" hose flowing 500 GPM

What is the friction loss of 100' of 1" hose with 100 gpm? Answer 100' of 1" hose flowing 100 GPM

What is the friction loss of 300' of 3" hose with 600 gpm? Answer 300' of 3" hose flowing 600 GPM

What is the friction loss of 400' of 3" hose with 800 gpm? Answer 400' of 4" hose flowing 800 GPM

Verify your own friction loss problems with Friction Loss Calculator

Friction Loss Explained

Friction loss occurs when water passes through a hose. Hose length, diameter, and GPM (volume) all affect friction loss. As water passes through a hose, friction between the water and the inside surface of the hose causes turbulence, which slows the water. The results in a PSI drop (pressure loss) at the other end of the hose. The higher the gpm passing through a hose, the more turbulance and friction loss will result.

Friction loss examples:

100 ft 1" @ 100 gpm = 150 PSI
100 ft 1 1/2" @ 100 gpm = 24 PSI
100 ft 1 3/4" @ 150 gpm = 34.88 PSI
200 ft 1 3/4" @ 150 gpm = 69.75 PSI
100 ft 1 3/4" @ 185 gpm = 53.05 PSI
200 ft 1 3/4" @ 185 gpm = 106.1 PSI
100 ft 1 3/4" @ 200 gpm = 62 PSI
200 ft 1 3/4" @ 200 gpm = 124 PSI
100 ft 2 1/2" @ 150 gpm = 4.5 PSI
100 ft 2 1/2" @ 200 gpm = 8 PSI
100 ft 2 1/2" @ 300 gpm = 18 PSI
200 ft 2 1/2" @ 300 gpm = 36 PSI

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