Free Tool
Calculate friction loss, pump discharge pressure, and total system pressure for any hose layout. Free, mobile-friendly, no sign-up.
Each story = 5 PSI. Negative = below grade. High-rise? Type any number.
When water moves through fire hose, it creates friction against the inside wall of the hose. That friction costs you pressure. The longer the hose lay and the more water you push through it, the more pressure you lose before it reaches the nozzle.
As a pump operator, your job is to overcome that friction loss so the nozzle gets the pressure it needs to produce an effective fire stream. Pump too little and your crew gets a weak stream that won't knock the fire. Pump too much and you risk blowing the hose or injuring the nozzle operator.
The standard formula used across the fire service is:
FL = C × (Q ÷ 100)² × (L ÷ 100)
The coefficient (C) changes based on hose diameter. Smaller hose creates more friction. A 1¾" attack line has a coefficient of 15.5, while a 2½" supply line is only 2. That's why flowing 200 GPM through a 1¾" line costs way more pressure than flowing it through a 2½".
| Hose Size | Coefficient (C) |
|---|---|
| 1" | 150 |
| 1½" | 24 |
| 1¾" | 15.5 |
| 2" | 8 |
| 2½" | 2 |
| 3" (2½" couplings) | 0.8 |
| 3" (3" couplings) | 0.677 |
| 3½" | 0.34 |
| 4" | 0.2 |
| 5" | 0.08 |
Once you know your friction loss, you can calculate the total pump discharge pressure (PDP) your engineer needs to set:
PDP = NP + FL + EP
Standard nozzle pressure for a combination (fog) nozzle is 100 PSI. Smooth bore nozzles use 50 PSI for handlines and 80 PSI for master streams.
Elevation adds (or subtracts) 5 PSI per story. Operating on the 3rd floor? Add 10 PSI. Operating in the basement? Subtract 5 PSI. On level ground it's zero.
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