Friction loss per 100 feet of fire hose at common flow rates, using the standard IFSTA / NFA coefficient method. Print it, bookmark it, or build the mental math through practice.
Friction loss is the pressure a pump operator loses pushing water through hose. It is the largest and most variable part of the pump discharge pressure calculation. This chart gives friction loss per 100 feet of hose for the most common fire-service hose sizes and flow rates. Multiply by the number of 100-foot sections in your lay to get total hose friction loss.
FL = C × (Q / 100)2 × (L / 100)
Because flow is squared, it drives friction loss far more than length: doubling the gpm quadruples the loss, while doubling the length only doubles it.
| Hose Diameter | Coefficient C | Common Use |
|---|---|---|
| 1¾" | 15.5 | Primary interior attack handline |
| 2" | 8 | High-flow handline |
| 2½" | 2 | Big-line attack, master stream supply |
| 3" (with 2½" couplings) | 0.8 | Supply line, relay pumping |
| 4" | 0.2 | Large diameter supply (LDH) |
| 5" | 0.08 | Large diameter supply (LDH) |
Values are friction loss in psi for one 100-foot section at the listed flow. A dash means that flow is outside the hose's normal working range.
| Flow (gpm) | 1¾" | 2" | 2½" | 3" | 4" | 5" |
|---|---|---|---|---|---|---|
| 95 | 14 | 7 | — | — | — | — |
| 125 | 24 | 13 | 3 | — | — | — |
| 150 | 35 | 18 | 5 | 2 | — | — |
| 185 | 53 | 27 | 7 | 3 | — | — |
| 200 | 62 | 32 | 8 | 3 | — | — |
| 250 | — | 50 | 13 | 5 | 1 | — |
| 300 | — | — | 18 | 7 | 2 | 1 |
| 325 | — | — | 21 | 8 | 2 | 1 |
| 400 | — | — | 32 | 13 | 3 | 1 |
| 500 | — | — | 50 | 20 | 5 | 2 |
| 750 | — | — | — | 45 | 11 | 5 |
| 1000 | — | — | — | — | 20 | 8 |
| 1250 | — | — | — | — | 31 | 13 |
| 1500 | — | — | — | — | 45 | 18 |
Values rounded to the nearest psi from FL = C × (Q/100)2. Some departments use slightly different coefficients (for example a coefficient of 12 for 1¾" hose, or the condensed "Q" mental-math method for 2½"); always train to your department's adopted standard.
A crew pulls 200 feet of 2½" hose flowing 250 gpm. From the chart, 2½" at 250 gpm is 12.5 psi per 100 ft. Two sections means 2 × 12.5 = 25 psi of friction loss. Add that to nozzle pressure, elevation, and any appliance loss to find the pump discharge pressure for that line.
Use the free Fire Hose Friction Loss Calculator to compute any size, flow, and length instantly, then roll it into the Pump Discharge Pressure Calculator for the full PDP. New to the math? Start with How to Calculate Pump Discharge Pressure.
Every number on the chart comes from FL = C × (Q/100)² × (L/100): coefficient, flow in hundreds of GPM squared, length in hundreds of feet. Example: 200 ft of 1¾" flowing 150 GPM. C for 1¾" is 15.5, so FL = 15.5 × (1.5)² × 2 = 15.5 × 2.25 × 2 ≈ 70 PSI. Add a 100 PSI fog nozzle and your pump discharge pressure is 170 PSI — before elevation or appliances.
What is the friction loss per 100 feet of 1.75-inch hose? Using the standard coefficient of 15.5, 1.75-inch hose loses about 35 psi per 100 ft at 150 gpm and about 53 psi per 100 ft at 185 gpm. Friction loss = 15.5 x (gpm/100)^2 per 100 ft.
What are the fire hose friction loss coefficients? Standard IFSTA / NFA coefficients are: 1.75-inch = 15.5, 2-inch = 8, 2.5-inch = 2, 3-inch = 0.8, 4-inch = 0.2, and 5-inch = 0.08.
How do you read a friction loss chart? Find the row for your flow in gpm and the column for your hose diameter to get the friction loss in psi per 100 feet. Multiply that value by the number of 100-foot sections in your hose lay to get total hose friction loss.
Does flow or length affect friction loss more? Flow. Flow is squared in the formula, so doubling the gpm quadruples friction loss, while doubling the hose length only doubles it.
How much friction loss does 2.5-inch hose have at 250 gpm? About 12.5 psi per 100 feet (coefficient 2 x (250/100)^2 = 2 x 6.25 = 12.5). A 200-foot lay at that flow loses about 25 psi.