Fire Hose Friction Loss Calculator
Calculate estimated pressure loss through fire hose using hose size, water flow and hose length. The calculator uses the commonly used fire-service friction loss equation FL = C × Q² × L.
Calculate fire hose friction loss
Enter the hose size, flow rate and total hose length. Results are shown in pounds per square inch (PSI).
Hose details
Standard coefficients are general fire-service reference values. Actual hose performance can vary.
Results
Calculation
FL = 15.5 × 1.50² × 2.00 = 69.75 PSI
What is fire hose friction loss?
As water moves through a fire hose, friction between the moving water and the inside of the hose causes pressure to decrease. This pressure reduction is known as friction loss.
Friction loss increases rapidly as water flow increases. A longer hose line also produces greater total friction loss, while larger diameter hose generally produces much less resistance at the same flow rate.
Estimating this loss is an important part of fire-service hydraulics because sufficient pressure must remain available elsewhere in the water-delivery system.
Fire hose friction loss formula
A commonly used fire-service method expresses friction loss as:
- FL
- Friction loss in PSI
- C
- Friction-loss coefficient for the hose
- Q
- Flow rate in hundreds of gallons per minute
- L
- Hose length in hundreds of feet
For example, a flow of 150 GPM gives a Q value of 1.5. A hose length of 200 feet gives an L value of 2.
Fire hose friction-loss coefficients
The calculator uses the following general reference coefficients. These values provide a convenient method for estimating friction loss, but they should not be treated as measured performance data for every hose.
| Nominal hose size | Coefficient (C) |
|---|---|
| 1½ in | 24 |
| 1¾ in | 15.5 |
| 2 in | 8 |
| 2½ in | 2 |
| 3 in | 0.8 |
| 4 in | 0.2 |
| 5 in | 0.08 |
Important: hose construction, lining, age, condition and manufacturer specifications can affect actual friction loss. Use a manufacturer's measured coefficient when accurate hose-specific data is available.
Fire hose friction loss example
Suppose a 200-foot length of 1¾-inch hose is flowing 150 gallons per minute.
Hose coefficient: C = 15.5
Flow factor: Q = 150 ÷ 100 = 1.5
Length factor: L = 200 ÷ 100 = 2
Friction loss:
The estimated total pressure lost to friction through the 200-foot hose line is therefore approximately 69.75 PSI.
Why does flow rate have such a large effect?
Notice that Q is squared in the friction-loss equation. Consequently, friction loss does not increase in a simple one-to-one relationship with flow.
For the same hose and hose length, doubling the flow factor produces approximately four times the calculated friction loss:
This is one reason hose diameter and required flow are important considerations in fire-service water delivery.
What this calculator includes
This calculator estimates hose friction loss only. It does not calculate complete pump discharge pressure.
A complete fire-service hydraulic calculation can also involve factors such as:
- Nozzle pressure
- Elevation pressure
- Appliance losses
- Standpipe or sprinkler system requirements
- Hose configuration
- Actual hose condition and construction
Those factors should be evaluated separately when determining the pressure requirements of a complete water-delivery system.
Frequently asked questions
What does C mean in the fire hose friction loss formula?
C is the friction-loss coefficient assigned to a hose. It represents the resistance associated with a particular nominal hose size and hose characteristics. Lower coefficients generally indicate less friction resistance.
What does Q mean in fire-service hydraulics?
Q represents the water flow in hundreds of gallons per minute. For example, 100 GPM gives Q = 1, 150 GPM gives Q = 1.5, and 250 GPM gives Q = 2.5.
What does L mean in the friction loss equation?
L represents hose length in hundreds of feet. A 100-foot hose line has L = 1, 200 feet has L = 2, and 500 feet has L = 5.
Does doubling hose length double friction loss?
Under the CQ²L calculation, yes. If hose size and flow remain unchanged, doubling the hose length doubles the estimated total friction loss.
Does doubling flow double friction loss?
No. Because flow factor Q is squared, doubling Q produces approximately four times the calculated friction loss when hose size and length remain unchanged.
Is this the same as pump discharge pressure?
No. Hose friction loss is only one part of a complete pump discharge pressure calculation. Nozzle pressure, elevation and appliance losses may also need to be considered.
Calculation notes and references
The calculator uses the traditional fire-service CQ²L friction-loss method. The method is a simplified hydraulic relationship used for estimating pressure loss in fire hose.
Reference material for the calculation method includes fire-service hydraulic guidance and technical documentation describing the relationship between hose coefficient, flow and hose length.
Operational note: Results from this calculator are estimates for reference, education and planning. They are not a substitute for department SOPs/SOGs, manufacturer data, approved hydraulic procedures, field measurements or professional operational judgement.