Free fire hose friction loss calculator for pump operators. Enter your hose size, flow rate, and length to get instant friction loss in PSI — using the standard IFSTA / NFA coefficient formula taught for the NFPA 1002 pump operator standard. No login, no app. New to the math? Read the friction loss formula explained →
Friction loss is the pressure lost to turbulence as water moves through the hose. It grows with the square of the flow rate, so flow is the dominant factor.
The fire-service friction loss formula uses a coefficient for each hose diameter:
C is the hose coefficient, Q is flow in gpm, and L is hose length in feet. Doubling the flow quadruples the friction loss; doubling the length only doubles it.
| Hose diameter | Coefficient (C) |
|---|---|
| 1¾″ | 15.5 |
| 2″ | 8.0 |
| 2½″ | 2.0 |
| 3″ | 0.80 |
| 4″ | 0.20 |
| 5″ | 0.08 |
250 gpm through 200 ft of 2½″ hose (C = 2):
Precomputed friction loss per 100 ft of hose at common fireground flows, using the same IFSTA / NFA coefficients as the calculator. For longer lays, multiply by the number of hundred-foot sections. A printable wallet-card version is in the fire hose friction loss chart guide.
| Flow (gpm) | 1¾″ | 2″ | 2½″ | 3″ | 4″ | 5″ |
|---|---|---|---|---|---|---|
| 95 | 14.0 | 7.2 | 1.8 | 0.7 | 0.2 | 0.1 |
| 125 | 24.2 | 12.5 | 3.1 | 1.3 | 0.3 | 0.1 |
| 150 | 34.9 | 18.0 | 4.5 | 1.8 | 0.5 | 0.2 |
| 185 | 53.0 | 27.4 | 6.8 | 2.7 | 0.7 | 0.3 |
| 250 | 96.9 | 50.0 | 12.5 | 5.0 | 1.3 | 0.5 |
| 300 | — | 72.0 | 18.0 | 7.2 | 1.8 | 0.7 |
| 500 | — | — | 50.0 | 20.0 | 5.0 | 2.0 |
| 750 | — | — | 112.5 | 45.0 | 11.3 | 4.5 |
| 1000 | — | — | — | 80.0 | 20.0 | 8.0 |
Values in psi per 100 ft. Dashes mark flows beyond the practical range for that diameter. Attack-line flows above 250 gpm on 1¾″ hose produce unmanageable friction loss — which is exactly what the chart is for.
The scenario: 300 ft of 2½" hose flowing 250 GPM.
FL = C × (Q/100)² × (L/100) = 2.0 × (2.5)² × 3 = 2.0 × 6.25 × 3 = 37.5 PSI.
Now the argument for large-diameter hose in one line: the same 250 GPM through 300 ft of 5" (C = 0.08) loses just 1.5 PSI. Same water, 25× less friction — which is why supply lines are big and attack lines are maneuverable.
PumpForge drills these calculations into muscle memory on a realistic pump panel — 16 built-in scenarios, automatic scoring, after-action reports. Every station, any computer or tablet.
See the fire pump simulator →Coefficients per IFSTA / NFA. For training and estimation; always verify against your department SOPs. Related tools: pump discharge pressure, smooth bore flow, and required fire flow. Friction loss math is a core skill under NFPA 1002. Keep every pump-ops formula on one page with the fireground hydraulics cheat sheet.