Hazen-Williams · pressure loss per foot · fire protection piping
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Loss vs Flow
C-factors represent internal pipe roughness. Higher values mean smoother pipe and less friction loss. The values below are commonly used in fire protection hydraulic calculations.
| C-Factor | Pipe Material | Condition | Notes |
|---|
This calculator uses the Hazen-Williams equation to estimate friction loss (pressure drop) in piping systems. It is designed for fire protection engineers and designers who need quick friction loss checks during sprinkler system design, hydraulic analysis, or field troubleshooting.
Select a pipe size and schedule to auto-populate the internal diameter, or enter a custom ID. Choose a C-factor for the pipe material, enter the flow rate in GPM and the total pipe length (including equivalent lengths for fittings), and the calculator returns loss per foot, total loss, and flow velocity.
The Hazen-Williams formula is empirical and applies to water at roughly 40–75°F flowing in full pipes. It does not account for temperature extremes, antifreeze solutions, or compressible fluids. This calculator handles single pipe segments — for full system analysis, use hydraulic calculation software.
In fire sprinkler hydraulic calculations, friction loss is the primary driver of pressure demand beyond elevation. Designers must account for friction loss through every pipe segment from the water supply to the most remote sprinkler. The Hazen-Williams formula is the standard method used in NFPA 13 and NFPA 24 hydraulic calculations.
When entering pipe length, include equivalent lengths for fittings (elbows, tees, valves) in addition to straight pipe runs. Equivalent length tables are published in NFPA 13 and manufacturer literature. This calculator does not automatically add fitting losses — you must include them in the total length input.
Fire protection underground mains are governed by NFPA 24. The most common pipe materials for underground fire service mains include:
NFPA 13 specifies C = 120 for black steel (the most common fire sprinkler pipe material) and C = 150 for listed CPVC and copper tube. For existing systems with aged or corroded pipe, a lower C-factor (such as 100) may be more appropriate. Always verify with the project specifications and the authority having jurisdiction.
Equivalent length converts the friction loss through fittings (elbows, tees, reducers, valves) into an equivalent length of straight pipe that would produce the same loss. Add the equivalent lengths for all fittings to the straight pipe length to get the total equivalent length for a pipe segment.
The Hazen-Williams formula is empirical and works well for water in pipes from about ¾″ to 72″ at typical velocities. It is less accurate at very high velocities, for very small pipes, or for fluids other than water. For fire protection design, it is the accepted standard per NFPA 13.
Flow enters the Hazen-Williams formula raised to the 1.85 power, so friction loss increases roughly with the square of the flow rate. Doubling the flow through the same pipe roughly quadruples the friction loss. This is why pipe sizing decisions have such a large impact on system pressure demand.
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