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Pipe Roughness (ε) Table

Absolute roughness (ε) values for common pipe materials, in millimetres and feet. Absolute roughness drives the Darcy friction factor through the Colebrook-White equation and the Moody chart, used in the Darcy-Weisbach head-loss method. Values follow the Moody chart, Crane TP-410, and Colebrook.

Absolute Roughness by Material
Materialε (mm)ε (ft)Notes
Smooth — drawn & plastic
Drawn tubing — glass, brass, copper, aluminum0.00150.000005Effectively hydraulically smooth.
PVC / CPVC / plastic0.00150.000005Smooth bore; no aging.
Fiberglass (FRP / GRP)0.0050.000016Smooth resin bore.
HDPE / polyethylene (PE)0.0070.000023Fusion-welded.
Steel
Stainless steel0.0150.000049Smooth, corrosion-resistant.
Commercial / wrought steel (new)0.0450.00015Classic Moody value.
Galvanized iron / steel0.150.00049Zinc coating.
Riveted steel0.9 – 90.003 – 0.03Seam roughness; very rough.
Corroded / rusted steel0.15 – 40.0005 – 0.013Rises with age.
Iron
Asphalted cast iron0.120.0004Coated bore.
Cast iron (uncoated)0.260.00085Classic value; tuberculates.
Ductile iron (cement-lined)0.10.00033Lining smooths bore.
Concrete & masonry
Concrete, smooth / new0.30.001Steel-formed or cast.
Concrete, coarse / rough3.00.01Rough finish or aged.
Wood stave0.18 – 0.90.0006 – 0.003Legacy.
Brick / riveted / rubble1 – 100.003 – 0.03Masonry channels.

Values are typical reference figures; published ranges vary by source and pipe condition. Use a higher (aged) value for conservative, long-life design.

Relative Roughness & the Friction Factor

What actually controls turbulent friction is relative roughness — absolute roughness divided by the internal diameter, ε/D\varepsilon / D. The Darcy friction factor ff then comes from the Colebrook-White equation:

1f=−2log⁡10 ⁣(ε3.7 D+2.51Re f)\frac{1}{\sqrt{f}} = -2 \log_{10}\!\left( \frac{\varepsilon}{3.7\,D} + \frac{2.51}{Re\,\sqrt{f}} \right)

and the friction head loss from Darcy-Weisbach:

hf=f LD V22gh_f = f \, \frac{L}{D} \, \frac{V^2}{2g}
  • ε\varepsilon — absolute roughness (from the table above)
  • DD — internal diameter, VV — mean velocity
  • ReRe — Reynolds number, gg — gravitational acceleration

In laminar flow (Re<2300Re < 2300), f=64/Ref = 64/Re and roughness has no effect. Roughness only matters in turbulent flow.

Roughness vs Hazen-Williams C

Absolute roughness (Darcy-Weisbach) and the Hazen-Williams C-factor are two ways of describing the same thing — pipe smoothness — but they are not directly convertible. A lower ε corresponds to a higher C, yet the exact mapping depends on diameter and velocity because the two methods model friction differently.

Use absolute roughness with Darcy-Weisbach for any fluid (gases, oils, hot liquids) and across all flow regimes; use the Hazen-Williams C-factor for water at ambient temperature. SimuPipe's friction loss calculator and network solver support both, using these ε-values per material.

Frequently Asked Questions

What is absolute pipe roughness (ε)?
Absolute roughness (ε, sometimes written as e or k) is the average height of the surface irregularities on the inside wall of a pipe, expressed as a length — typically millimetres or feet. It feeds the Colebrook-White equation (and the Moody chart) to find the Darcy friction factor used in the Darcy-Weisbach head-loss formula. Smooth drawn copper or plastic is about 0.0015 mm; new commercial steel is about 0.045 mm; uncoated cast iron is about 0.26 mm.
What is the difference between absolute roughness (ε) and relative roughness (ε/D)?
Absolute roughness ε is a fixed property of the pipe material and condition. Relative roughness is the dimensionless ratio ε/D — absolute roughness divided by the internal diameter — and it is what actually controls the friction factor in turbulent flow. The same ε produces much higher friction in a small pipe than in a large one, so always compare ε against the pipe diameter, not in isolation.
What roughness value should I use for steel pipe?
For new commercial or wrought steel, use ε = 0.045 mm (0.00015 ft) — the classic Moody-chart value, which is also SimuPipe's default for carbon steel. Stainless steel is smoother at about 0.015 mm. Galvanized steel is rougher at about 0.15 mm. For old, corroded, or scaled steel, use a higher value (0.15–4 mm) to stay conservative, because roughness grows over the life of the line.
How does pipe roughness change with age?
It increases. Corrosion, scaling, and tuberculation build up on the wall over time, raising ε and therefore friction loss — uncoated cast iron and unlined steel can rise several-fold over decades. Plastic, fiberglass, and lined pipes are stable and keep their as-new roughness. For long-life design, size with an aged roughness value rather than the new-pipe figure.
Should I use roughness (Darcy-Weisbach) or the Hazen-Williams C-factor?
Use absolute roughness with Darcy-Weisbach / Colebrook-White when the fluid is anything other than water, when temperature varies, or when you need a rigorous result across all flow regimes — it accounts for viscosity and Reynolds number. Use the Hazen-Williams C-factor for water at ambient temperature in turbulent flow, where it is the simpler convention. The two describe the same smoothness differently and are not directly interchangeable — see our Hazen-Williams C-factor table for the equivalent values.
Why does roughness barely matter in laminar flow?
In laminar flow (Reynolds number below about 2300) the Darcy friction factor is simply 64/Re and does not depend on roughness at all — the slow-moving viscous layer at the wall hides the surface texture. Roughness only affects friction in turbulent flow, where ε/D and Reynolds number together set the friction factor via the Colebrook-White equation and the Moody chart.

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