Calculator Inputs
Use one overall page flow. The form below switches between nozzle, density, or combined design logic.
Plotly Graph
The graph compares demand methods and available supply flow.
Formula Used
Flow per nozzle = K × √P
Total nozzle flow = Number of open nozzles × Flow per nozzle
Density flow = Design density × Design area
Base demand = Governing method flow + Hose allowance
Final demand = Base demand × (1 + Safety factor ÷ 100)
Friction loss (psi) = 4.52 × L × Q1.85 ÷ (C1.85 × d4.87)
Elevation loss (psi) = Elevation rise × 0.433
Required supply pressure = Nozzle pressure + Friction loss + Elevation loss
Velocity (ft/s) = 0.4085 × Q ÷ d2
This page gives an engineering estimate for deluge demand, pressure, and velocity. Final fire protection design should always be checked against the applicable standard, the listed nozzle, the protected hazard, and the authority having jurisdiction.
How to Use This Calculator
- Select the calculation mode. Use combined mode when you want the larger of nozzle flow and density-area flow to govern.
- Enter the number of open nozzles, the listed K-factor, and the target residual nozzle pressure.
- Enter density and area values if you want a cross-check against area-based water demand.
- Add hose allowance and a safety factor to reflect extra demand margin.
- Fill in pipe length, inside diameter, and C-factor to estimate friction loss.
- Enter elevation rise, available pressure, and available flow to compare demand against supply.
- Press the calculate button to show the result block above the form.
- Use the CSV and PDF buttons after calculation to export the result summary.
Example Data Table
| Scenario | Open Nozzles | K-Factor | Nozzle Pressure | Density | Area | Final Demand | Required Pressure |
|---|---|---|---|---|---|---|---|
| Transformer exposure | 12 | 5.6 | 20 psi | 0.30 gpm/ft² | 2,000 ft² | 941.85 gpm | 45.68 psi |
| Loading rack spray | 18 | 5.6 | 25 psi | 0.35 gpm/ft² | 2,400 ft² | 1,441.82 gpm | 75.29 psi |
| Cable tray protection | 10 | 4.2 | 15 psi | 0.20 gpm/ft² | 1,500 ft² | 605.00 gpm | 28.90 psi |
Frequently Asked Questions
1) What does this deluge flow calculator estimate?
It estimates total water demand, nozzle flow, density-area demand, pipe friction loss, velocity, required supply pressure, and remaining supply margin for a deluge-style water spray layout.
2) When should I use nozzle mode instead of density mode?
Use nozzle mode when your design is driven by listed nozzle discharge and residual pressure. Use density mode when your project is based on a required water application rate over a specific area.
3) Why does combined mode choose the larger flow?
Combined mode is conservative. It compares nozzle-based and density-area demand, then uses the larger value before adding hose allowance and safety factor.
4) What is the K-factor in this calculator?
K-factor is the nozzle discharge constant. Higher K-factors pass more water at the same pressure. The calculator uses it directly with the square-root pressure relation.
5) Why is pipe diameter important?
Pipe diameter strongly affects friction loss and flow velocity. A small diameter can raise losses quickly, increase required supply pressure, and create poor hydraulic margins.
6) Does this replace a full fire protection hydraulic calculation?
No. It is a planning and checking tool. Final design should be verified against the applicable standard, the listed nozzle, the hazard details, and the authority having jurisdiction.
7) Why is there an outdoor pressure warning?
Outdoor water spray systems often need higher residual pressure at the nozzle than some indoor arrangements. The warning reminds you to confirm the required minimum for the exact hazard and nozzle listing.
8) What do pressure margin and flow margin mean?
Pressure margin compares available supply pressure with estimated required pressure. Flow margin compares available water flow with final demand. Positive margins indicate the supply currently exceeds the estimate.