Configure Your Hose Lay

Quick Presets
Nozzle & Lines
Fog=100 · Smooth bore=50 · Master stream=80
Attack Line
Supply Line (optional)
Elevation
±0.434 psi/ft · High-rise: +5 psi/floor (~10 ft)
Appliance Friction Loss
AllFirefighter — PDP Calculator · allfirefighter.com/tools/pdp-calculator
Estimated Pump Discharge Pressure
—
Total Flow
—
Elevation
—
Appliance
—
Pressure Breakdown
Nozzle Pressure (NP)—
FL — Supply line—
FL — Attack line—
Appliance loss—
Elevation—
PDP—
Use with these tools:
📊 Pump Chart Generator💧 Friction Loss🔥 Fire Flow (NFF)🚰 Hydrant Flow🚨 MAYDAY LUNAR
Training estimate only. Local SOP/SOG, nozzle specifications, hose conditions, and appliance characteristics affect actual pressures. Always verify against your department's tested pump charts before operational use.
Generated by allfirefighter.com/tools/pdp-calculator — Training use only. Follow your department SOP.

What Is Pump Discharge Pressure (PDP)?

Pump Discharge Pressure (PDP) is the total pressure a fire pump must generate at the pump outlet to deliver the correct nozzle pressure at the end of the hose lay — overcoming friction losses, appliance resistance, and elevation change. On level ground with no appliances: PDP = NP + FL(attack). Add supply line FL, appliance losses, and elevation as they apply.

PDP is what the driver/engineer sets on the pump panel discharge gauge. Setting it too low means the nozzle person has insufficient pressure — poor reach, poor penetration, potential victim exposure. Setting it too high risks hose whipping, coupling failure, nozzle control problems, and firefighter injury. Accurate PDP is therefore not a bureaucratic exercise — it is a safety-critical calculation that every pump operator must be able to perform quickly and correctly.

This calculator allows you to compute PDP for any hose lay configuration in seconds — from a simple single-line fog attack to a standpipe operation with multiple floors of elevation and appliance losses.

The PDP Formula Explained

PDP = NP + FLsupply + FLattack + Appliance Loss + Elevation
Where FL = C × Q² × L  (Q = GPM ÷ 100, L = length ÷ 100)
NPNozzle Pressure

Required pressure at the nozzle outlet. Combination fog: 100 psi. Smooth bore handline: 50 psi. Smooth bore master stream: 80 psi. Fog master stream: 100 psi. Always verify with your nozzle manufacturer specs and department SOP.

FLFriction Loss

Pressure lost to hose wall friction. Calculated separately for supply (total flow) and attack (per-line flow). FL = C × (GPM/100)² × (ft/100). Doubles when length doubles; quadruples when GPM doubles.

AFLAppliance Loss

Pressure lost through fittings and devices: wyes (10 psi), standpipes (25 psi), master stream devices (10 psi). These are average values — actual losses vary with device design and flow rate.

ElevElevation

Water weighs 0.434 psi per foot of vertical rise. Add this for uphill lays; subtract for downhill. High-rise rule of thumb: +5 psi per floor. This is separate from friction loss and must be calculated independently.

Multi-Line Attack PDP — Wye Operations

When a wye or gated wye splits a single supply line into two or more attack lines, the PDP calculation has an important detail: the supply line carries the total combined flow (GPM per line × number of lines), while each attack line carries only its individual flow for friction loss calculation.

Example: 2-Line Attack via Wye

  • 2 × 1¾" lines, 150 GPM each, 200 ft each
  • 3" supply line, 300 ft from pump to wye
  • NP = 100 psi, AFL (wye) = 10 psi
  • Total supply flow = 150 × 2 = 300 GPM
  • FL supply (300 GPM/300ft/3") = 0.8 × 9 × 3 = 21.6 psi
  • FL attack (150 GPM/200ft/1¾") = 15.5 × 2.25 × 2 = 69.8 psi
  • PDP = 100 + 21.6 + 69.8 + 10 = 201 psi → 205 psi suggested

Why attack FL is per-line, not total

Each attack line runs at its individual flow rate. The pump delivers NP + FL of the one line's resistance — both lines see the same pressure at the wye outlet and each line's FL is identical (same length, diameter, and flow). If you doubled attack FL, you would be double-counting a resistance that the pump only needs to overcome once for each line from the wye outward.

Driver/engineer note: If attack lines are different lengths or different diameters, calculate PDP for the highest-demand line (longest or highest elevation) and set the pump to that pressure. Use gate valves at the wye to throttle the lower-demand lines.

Elevation Correction in PDP

Elevation is the most frequently forgotten component of PDP calculations — especially in the chaos of early incident operations. A 20-foot building with the attack team on the second floor adds roughly 10 psi to PDP. That same oversight at 80 feet (about an 8-story building) is 35 psi — nearly equivalent to 200 feet of 1¾" hose at 150 GPM.

ScenarioElevation (ft)Pressure adjustmentNotes
Flat ground0+0.00 psiNo correction
1 floor (10 ft)+10+4.34 psi~5 psi rounded
2 floors (20 ft)+20+8.68 psi~10 psi rounded
5 floors (50 ft)+50+21.70 psi~22 psi
10 floors (100 ft)+100+43.40 psi~45 psi
Downhill (-20 ft)-20-8.68 psiSubtract from PDP

Worked Examples — Step by Step

1¾" Fog / 150 GPM / 200 ft
1NP = 100 psi (fog nozzle)
2FL attack: C=15.5, Q=1.5, L=2 → 15.5 × 2.25 × 2 = 69.75 psi
3No supply, no appliance, no elevation
4PDP = 100 + 69.75 = 169.75 → 170 psi suggested
1¾" Smooth Bore / 160 GPM / 200 ft
1NP = 50 psi (smooth bore handline)
2FL attack: C=15.5, Q=1.6, L=2 → 15.5 × 2.56 × 2 = 79.36 psi
3No supply, no appliance, no elevation
4PDP = 50 + 79.36 = 129.36 → 130 psi suggested
2-Line / Wye / 3" supply 300 ft
1NP = 100 psi · Lines = 2 · 150 GPM each
2Supply FL: C=0.8, Q=3.0 (300 total), L=3 → 0.8 × 9 × 3 = 21.6 psi
3Attack FL (per line): C=15.5, Q=1.5, L=2 → 69.75 psi
4Wye AFL = 10 psi
5PDP = 100 + 21.6 + 69.75 + 10 = 201.35 → 205 psi
Standpipe — Floor 2 / 150 GPM
1NP = 100 psi · Attack: 2½" 100 ft
2Supply: 3" 200 ft to FDC
3Elevation: floor 2 ≈ 20 ft = 0.434×20 = 8.7 psi
4AFL: Standpipe = 25 psi
5PDP = 100 + FLS + FLA + 25 + 8.7 → ~175 psi

PDP Calculator FAQ

PDP is the total pressure a fire pump must generate at the pump outlet to deliver correct nozzle pressure at the end of the hose lay — overcoming friction losses in supply and attack lines, appliance resistance, and elevation change. It is what the driver/engineer sets on the pump panel discharge gauge.

PDP = NP + FL(supply) + FL(attack) + Appliance Loss + Elevation. Where FL = C × (GPM/100)² × (length/100). NP is nozzle pressure; C is the hose coefficient (e.g. 15.5 for 1-3/4 inch); elevation adds or subtracts 0.434 psi per foot.

FL = 15.5 × (1.5)² × 2 = 69.75 psi. NP = 100 psi. PDP = 100 + 70 = 170 psi on level ground, no appliances. Suggested setting: 170 psi.

The supply line carries total combined flow (GPM × lines). Each attack line carries its individual flow. PDP = NP + FL_supply(total GPM) + FL_attack(per-line GPM) + appliance + elevation. This calculator handles this correctly automatically.

Water weighs 0.434 psi per foot of vertical rise. Every foot uphill adds resistance the pump must overcome in addition to friction. For every foot of elevation gain, add 0.434 psi. For downhill lays, subtract 0.434 psi per foot. High-rise: +5 psi per floor above the pumper.

The standard coefficient (C) for 1-3/4 inch hose is 15.5. Note: the original AllFirefighter calculator used 15 — this has been corrected to 15.5 per IFSTA references. Other common values: 1.5 inch = 24, 2.5 inch = 2, 3 inch = 0.8, 4 inch = 0.2, 5 inch LDH = 0.08.

A typical standpipe or FDC connection friction loss is 25 psi per IFSTA references. This accounts for system piping resistance from the FDC to the standpipe riser. Combined with elevation to upper floors, standpipe PDP can exceed 200 psi on upper floors — verify your department's maximum pump pressure and SOP.

PDP is the pressure at the pump outlet — what the driver sets on the discharge gauge. Residual pressure is the pressure measured at a flowing hydrant, indicating available water supply capacity. They are separate measurements at different points in the water delivery system.
Training reference only. Always follow your department SOP/SOG and IFSTA/NFPA references. Editorial policy · Our authors