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 hand methods described below); 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 the friction loss formula works, then 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.
The chart above is exact. The condensed Q formula is what you use when there is no chart, no calculator and no time — a hand method that gets you close enough to set a pump using numbers you can square in your head. Q is simply the flow divided by 100. 250 gpm is a Q of 2.5. 500 gpm is a Q of 5.
It is defined for supply-line diameters — 3", 4" and 5" hose. Each size is the same squared figure with a different divisor:
| Hose | Friction loss per 100 ft |
|---|---|
| 3" | FL = Q² |
| 4" | FL = Q² ÷ 5 |
| 5" | FL = Q² ÷ 15 |
Multiply the result by the number of 100-ft sections to get the loss for the whole lay. The 3" form works for either 2½" or 3" couplings.
600 ft of 3" flowing 500 gpm. Q = 5, so Q² = 25 psi per 100 ft. Six sections: 25 × 6 = 150 psi. Two squares and one multiplication, no chart required.
The same lay in 5". Q² ÷ 15 = 25 ÷ 15 ≈ 1.7 psi per 100 ft, so about 10 psi over the whole 600 ft. That gap — 150 psi against 10 — is the entire argument for large-diameter supply line, and you can do it in your head at the hydrant.
For 3" hose, IFSTA notes the condensed Q result runs roughly 20 percent above what the full FL = CQ²L method gives. That is not sloppiness — the errors are not symmetrical. A line pumped a little high is uncomfortable; a line pumped low is a crew working behind a stream that will not reach. When you round in your head, round up.
The condensed Q formula does not cover attack lines — it is a supply-line method. For 2½" the traditional hand method is the Underwriters’ formula, FL = 2Q² + Q per 100 ft (below 100 gpm, add only half a Q). At 250 gpm: Q = 2.5, so FL = (2 × 6.25) + 2.5 = 15 psi per 100 ft, against 12.5 psi from the chart — high again, and deliberately so.
For 1¾" there is no clean mental shortcut worth trusting. The coefficient is large enough that small flow errors move the answer a long way, so use the chart above or the calculator.
NFPA 1002 skills evaluations expect the coefficient method, FL = CQ²L. Learn the hand method for the fireground and the full formula for the exam — they answer different questions. Run any lay both ways with the free Fire Hose Friction Loss Calculator to see how far apart they land.
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.
What is the condensed Q formula? It is a fireground shortcut for friction loss in supply lines, where Q is the flow divided by 100. Per 100 feet: 3-inch hose is Q², 4-inch is Q² divided by 5, and 5-inch is Q² divided by 15. Multiply by the number of 100-foot sections for the full lay. For 3-inch hose the result runs roughly 20 percent above the full FL = CQ²L method, which errs toward more pressure rather than less.
What is the condensed Q formula for 3 inch hose? FL = Q² per 100 feet, where Q is gpm divided by 100. For 600 feet of 3-inch flowing 500 gpm: Q = 5, Q² = 25 psi per 100 ft, times six sections = 150 psi. The same form is used whether the hose has 2½-inch or 3-inch couplings.