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Hazen-Williams C-Factor Table

Hazen-Williams roughness coefficients (C) for common pipe materials, with both new-pipe and conservative aged (design) values. The C-factor sets the friction loss in the Hazen-Williams equation, the standard method for water-distribution, fire-protection, and irrigation piping. Values follow Crane TP-410, AWWA, and Williams & Hazen.

C-Factor by Material
MaterialC (new / clean)C (design / aged)Notes
Plastic & lined pipe (smooth, minimal aging)
PVC / CPVC150150Smooth bore; effectively no aging.
HDPE / polyethylene (PE)150150Fusion-welded; no tuberculation.
Fiberglass (FRP / GRP)150150Smooth resin bore.
Cement-mortar–lined ductile iron140130Most common potable-water main.
Asbestos cement140140Legacy; smooth and stable.
Steel
Steel, new (welded / seamless)150120Unlined; corrodes over time.
Steel, cement-mortar lined140135Lining resists corrosion.
Galvanized iron / steel120120Zinc coating; moderate roughness.
Riveted steel110100Seam roughness lowers C.
Corrugated steel6060Very rough; culverts / drainage.
Copper, brass & stainless
Copper / brass150140Very smooth; slight scale over time.
Stainless steel150140Corrosion-resistant, smooth.
Cast & ductile iron (unlined)
Ductile iron, new unlined130120Modern; usually cement-lined instead.
Cast iron, new unlined130100Tuberculates with age — see below.
Cast iron, ~20 yr—95Internal tuberculation reduces C.
Cast iron, ~40 yr—75Heavily tuberculated.
Concrete & masonry
Concrete, new (smooth)140130Steel-form or centrifugally cast.
Concrete, average / old120110Rougher finish or aged.
Vitrified clay130110Gravity sewers.
Brick sewer100100Rough masonry.
Wood stave120110Legacy.

Values are typical reference figures; published ranges vary by source and pipe condition. Use the design column for sizing.

The Hazen-Williams Equation

In SI units, head loss from friction over a length of pipe is:

hf=10.67 L Q1.852C1.852 D4.87h_f = \frac{10.67 \, L \, Q^{1.852}}{C^{1.852} \, D^{4.87}}
  • hfh_f — head loss (m)
  • LL — pipe length (m)
  • QQ — volumetric flow rate (m³/s)
  • CC — Hazen-Williams coefficient (dimensionless, from the table above)
  • DD — internal pipe diameter (m)

Because CC sits in the denominator raised to the 1.852 power, head loss is roughly inversely proportional to C1.852C^{1.852} — dropping C from 150 to 100 increases friction loss by about 110% for the same flow.

Effect of Age — Unlined Cast Iron

Unlined metal pipe tuberculates as it corrodes, so its C-factor falls steadily with age. The classic Williams & Hazen / Lamont curve for unlined cast iron:

Pipe ageC-factor
New130
5 years120
10 years110
20 years95
30 years85
40 years75
When to Use Hazen-Williams

Hazen-Williams is an empirical formula calibrated for water at normal ambient temperature in turbulent flow. It is quick, needs only one roughness parameter (C), and is the convention in municipal water supply, fire sprinkler design (NFPA 13), and irrigation.

Switch to Darcy-Weisbach (with Colebrook-White) when the fluid is not water — gases, oils, or chemicals — when temperature varies widely, or when you need a physically rigorous answer across all flow regimes. Darcy-Weisbach accounts for fluid viscosity and Reynolds number; Hazen-Williams does not, which is why it must not be used for compressible (gas) flow.

SimuPipe supports both methods. The friction loss calculator lets you switch between Hazen-Williams and Darcy-Weisbach, and the full network solver uses these C-values per material.

Frequently Asked Questions

What is the Hazen-Williams C-factor?
The C-factor (also called the Hazen-Williams coefficient or roughness coefficient) is a dimensionless number that describes how smooth the inside of a pipe is for water flow. Higher values mean a smoother pipe and less friction loss: plastic pipe is around 150, new steel around 140-150, and old tuberculated cast iron can drop below 80. It is used in the Hazen-Williams equation to predict head loss or flow rate in water-distribution and fire-protection systems.
Does the C-factor increase or decrease as a pipe ages?
It decreases. As metal pipes corrode and tuberculate (build up internal deposits), the effective roughness rises and C falls — unlined cast iron can drop from about 130 when new to 75 or lower after 40 years. Plastic, fiberglass, and cement-lined pipes resist this and hold their C-value over the life of the line. For design you should use the lower, aged C-value rather than the new-pipe value.
When should I use Hazen-Williams instead of Darcy-Weisbach?
Use Hazen-Williams for water (and water-like fluids) at roughly normal ambient temperature in turbulent flow — its typical home is municipal water distribution, fire-protection, and irrigation. Use Darcy-Weisbach when the fluid is not water (gases, oils, chemicals), when temperature varies widely, or when you need a physically rigorous result across all flow regimes, because Darcy-Weisbach (via the Colebrook-White friction factor) accounts for fluid viscosity and Reynolds number while Hazen-Williams does not.
Which C-factor should I use for design?
Use the conservative (aged) value, not the new-pipe value, so the system still meets flow and pressure targets late in its life. Common design choices are 150 for PVC/HDPE, 130-140 for cement-lined ductile iron, 120 for steel and galvanized iron, and 100 or lower for old unlined cast iron. SimuPipe's friction-loss tool and solver use these same design defaults per material.
Is the Hazen-Williams equation valid for any fluid?
No. Hazen-Williams is an empirical formula calibrated specifically for water at around 4-25 °C. It has no viscosity term, so it is not valid for gases, oils, slurries, or hot fluids, and it loses accuracy at very high or very low velocities. For compressible (gas) flow or non-water liquids, use the Darcy-Weisbach method instead — SimuPipe blocks Hazen-Williams for compressible fluids for exactly this reason.
How does the C-factor relate to absolute roughness (ε)?
They describe the same physical idea — pipe smoothness — but are not directly interchangeable. A higher C corresponds to a lower absolute roughness ε used in Darcy-Weisbach, but the relationship depends on diameter and velocity because the two methods model friction differently. As a rough guide, C ≈ 150 is comparable to very smooth plastic (ε ≈ 0.0015 mm) and C ≈ 100 to corroded iron (ε ≈ 0.3-1 mm). When precision matters, size with Darcy-Weisbach and a roughness value rather than converting between the two.

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