Pump Discharge Pressure Calculator
Compute pump discharge pressure (PDP) using the same engine that powers the Fire Pump Simulator. Enter nozzle pressure, friction loss, and elevation — or let the calculator derive friction loss from your hose diameter, length, and target flow.
Pump Discharge Pressure
PDP = NP + FL + Elevation, computed by the same engine the simulator uses.
Nozzle height above the pump — ~10 ft per story. Adds 0.434 psi/ft.
The PDP equation
Pump discharge pressure is the gauge pressure the pump must deliver to put water out of the nozzle at the right pressure and flow. It’s the sum of three things:
PDP = NP + FL + Elevation
Nozzle pressure (NP)
The pressure the nozzle is rated for. Smooth bore handlines typically operate at 50 psi (345 kPa). Combination nozzles typically operate at 100 psi (700 kPa). Smooth bore master streams are commonly 80 psi (550 kPa). Use the rated value for the nozzle in service — it’s a constant for the operator, not a derived number.
Friction loss (FL)
Friction loss is the pressure the pump has to overcome to push water through the hose. It scales with the square of the flow, so doubling the flow quadruples the friction loss in the same hose.
Friction coefficients
These are the coefficient values used by the calculator and the simulator. They reflect typical NFPA values used in fireground hydraulics training.
| Hose | C (imperial) | C (metric) |
|---|---|---|
| 1½″ attack38 mm | 24 | 0.379 |
| 1¾″ attack45 mm | 15.5 | 0.245 |
| 2½″65 mm | 2 | 0.0316 |
| 3″77 mm | 0.678 | 0.0107 |
| 4″ supply100 mm | 0.2 | 0.00316 |
| 5″ LDH125 mm | 0.08 | 0.00126 |
Elevation loss
Every foot the nozzle is above the pump adds about 0.434 psi (9.81 kPa per meter). A common rule of thumb is roughly 5 psi per story. If the nozzle is below the pump, this term goes negative — but most fireground operations work upstairs, not downstairs.
Practice these calculations on a real-feel pump
The same engine that powers this calculator drives a full virtual fire pump simulator. Connect hydrants, static sources, and relays. Operate the pump. Review every action.