Calculate friction loss and pressure requirements using Hazen-Williams formula per NFPA 13/14 standards.
| Black Steel (Unlined) | C=100 |
| Galvanized Steel | C=120 |
| Stainless Steel | C=140 |
| Copper Tube | C=150 |
Enter flow, pipe size, and length,
then click "Calculate Pressure Loss"
The Hazen-Williams equation is the standard method for calculating friction loss in fire protection piping systems. It's specifically designed for water flow and is required by NFPA 13 for sprinkler system hydraulic calculations.
P = 4.52 × Q^1.85 / (C^1.85 × d^4.87)
Where: P = pressure loss (psi/ft), Q = flow (GPM), C = friction factor, d = internal diameter (inches)
The C-factor represents pipe roughness and varies by material and age:
| Pipe Material | C-Factor | Application |
|---|---|---|
| New Steel (Sch 40) | 120 | Standard sprinkler systems |
| Cement Lined Ductile Iron | 140 | Underground mains |
| CPVC/Plastic | 150 | Light hazard systems |
| Copper Tube | 150 | Special applications |
| Old Steel (15+ years) | 100 | Existing systems |
Minimum Pressure: Most sprinklers require 7 psi minimum operating pressure at the most remote sprinkler.
Velocity Limits: Water velocity should not exceed 32 ft/s to prevent water hammer and excessive noise.
Safety Factor: Add 10% safety margin to calculated pump pressure for system reliability.
For every foot of elevation rise, add 0.433 psi to account for static head. Conversely, subtract for elevation drops. This is critical for multi-story buildings and roof-mounted equipment.
Fittings create additional friction losses expressed as equivalent pipe lengths. Common values:
• 90° Elbow: 6-10 ft equivalent | • 45° Elbow: 3-5 ft | • Tee (flow through): 1-2 ft | • Tee (branch): 12-20 ft | • Gate Valve: 1-2 ft | • Check Valve: 15-25 ft