Pipe Roughness Values
Absolute roughness of common pipe materials, with relative roughness for 50, 100 and 200 mm pipe.
In turbulent flow the friction in a pipe depends on how rough the wall is compared with the pipe diameter. The absolute roughness (ε, in millimeters) is a typical height of the wall’s surface bumps; dividing by the inside diameter gives the relative roughness ε ÷ D, which goes into the Moody chart and the Colebrook equation.
The table
| Pipe material | Roughness, lowest (mm) | Roughness, highest (mm) | Typical roughness (mm) | Typical roughness (in) | Relative roughness for a 50 mm pipe | Relative roughness for a 100 mm pipe | Relative roughness for a 200 mm pipe |
|---|---|---|---|---|---|---|---|
| Drawn tubing: copper, brass, glass, plastic | 0.0015 | 0.0015 | 0.0015 | 6E-5 | 3E-5 | 2E-5 | 1E-5 |
| PVC and polyethylene pipe | 0.0015 | 0.007 | 0.0032 | 0.00013 | 6E-5 | 3E-5 | 2E-5 |
| Stainless steel, drawn | 0.015 | 0.015 | 0.015 | 0.00059 | 0.0003 | 0.00015 | 8E-5 |
| Commercial or welded steel, new | 0.045 | 0.046 | 0.0455 | 0.00179 | 0.00091 | 0.00045 | 0.00023 |
| Asphalted cast iron | 0.12 | 0.12 | 0.12 | 0.00472 | 0.0024 | 0.0012 | 0.0006 |
| Galvanized iron | 0.15 | 0.15 | 0.15 | 0.00591 | 0.003 | 0.0015 | 0.00075 |
| Cast iron, new | 0.25 | 0.26 | 0.255 | 0.01004 | 0.0051 | 0.00255 | 0.00127 |
| Wood stave | 0.18 | 0.9 | 0.4025 | 0.01585 | 0.00805 | 0.00402 | 0.00201 |
| Concrete | 0.3 | 3 | 0.9487 | 0.03735 | 0.01897 | 0.00949 | 0.00474 |
| Riveted steel | 0.9 | 9 | 2.846 | 0.11205 | 0.05692 | 0.02846 | 0.01423 |
Source and notes: Absolute roughness of commercial pipe (Moody, 1944; Crane TP-410; Cengel and Cimbala, Fluid Mechanics, Table 8-2). The typical value is the geometric mean of the range; relative roughness = roughness / inside diameter. Old pipe is much rougher than new: corrosion and deposits can raise the roughness several times.
How to use this table
- Find the pipe material and note the typical roughness.
- Divide by the inside diameter of your pipe (or read the relative roughness for 50, 100 and 200 mm).
- Use ε ÷ D and the Reynolds number to find the friction factor, or enter the roughness in the pipe flow calculator.
Worked example: friction factor for a 100 mm pipe at Re = 100 000
- Steel: ε = 0.0455 mm, so ε ÷ D = 4.550E-4. The Swamee-Jain equation f = 0.25 ÷ [log₁₀(ε/3.7D + 5.74/Re⁰·⁹)]² gives f = 0.0202.
- PVC: ε = 0.0032 mm, ε ÷ D = 3.200E-5, f = 0.0181, 11 percent lower than steel.
Notes and cautions
- New pipe is smoother than old. Corrosion, scale and growth can raise the roughness several times; design for the pipe in 10 to 20 years’ time.
- Roughness values from different sources differ by 10 to 20 percent. The table gives the commonly used value.
- For laminar flow the roughness does not matter: the friction factor is 64 ÷ Re.
Related tools and guides
- Pipe Flow and Pressure Drop Calculator
- Pipe Friction and the Moody Diagram (guide)
- Steel Pipe Sizes (NPS and DN, Schedule 40 and 80)
- Fitting and Valve Loss Coefficients (K Factors)
- All reference tables
FAQ
What is the roughness of commercial steel pipe?
0.045 mm (0.0018 inch) when new. Galvanized iron is 0.15 mm and cast iron 0.26 mm.
What is relative roughness?
The absolute roughness divided by the pipe inside diameter (ε ÷ D). It is the number the Moody chart is plotted against.
Sources
- Moody, “Friction factors for pipe flow”, Trans. ASME (1944); Crane Technical Paper 410; Cengel and Cimbala, Fluid Mechanics, Table 8-2. Swamee-Jain: J. Hydraulics Div. ASCE (1976).
- Absolute roughness of commercial pipe (Moody, 1944; Crane TP-410; Cengel and Cimbala, Fluid Mechanics, Table 8-2). The typical value is the geometric mean of the range; relative roughness = roughness / inside diameter. Old pipe is much rougher than new: corrosion and deposits can raise the roughness several times.