Choose roughness for the wetted surface
Absolute roughness ε is an effective internal wall roughness used in pipe friction models. Relative roughness ε/D divides it by the actual inside diameter.
Use these typical values for preliminary work with clean pipe. Match the material, lining, finish, and service condition before applying a value.
Browse material values ↓ · Convert a value / calculate ε/D ↓
Typical absolute roughness
Metric values below follow Pipe Flow Software. EPA’s new-pipe values are shown for comparison after conversion from 10⁻³ ft. Small differences reflect source rounding. Converted digits do not imply measurement precision.
| Material / surface | ε (mm) | ε (in) | ε (ft) | Source comparison (mm) |
|---|---|---|---|---|
| Cast iron, asphalt coated | 0.12 | 0.00472441 | 0.000393701 | Pipe Flow |
| Cast iron, uncoated | 0.26 | 0.0102362 | 0.000853018 | Pipe Flow; EPA ≈0.259 |
| Commercial or welded steel | 0.045 | 0.00177165 | 0.000147638 | Pipe Flow; EPA ≈0.0457 |
| Concrete / concrete lined | 0.3–3 | 0.011811–0.11811 | 0.000984252–0.00984252 | Pipe Flow; EPA ≈0.305–3.05 |
| Galvanized iron | 0.15 | 0.00590551 | 0.000492126 | Pipe Flow; EPA ≈0.152 |
| PVC, glass, drawn tubing | 0.0015 | 5.90551e-05 | 4.92126e-06 | Pipe Flow; EPA plastic ≈0.00152 |
No materials match your search.
Stainless steel, HDPE, sanitary tubing, and proprietary linings: use documented hydraulic roughness for the actual product and finish. This table does not assign an unverified universal value to those materials.
Convert roughness and calculate ε/D
Compare both ends for sensitivity. Choose a project value based on the actual surface condition.
How to use these values
- Select a value for the actual internal surface. A lined pipe follows the lining, not the metal underneath.
- Enter ε in the calculator’s selected roughness unit. Enter ε/D only when the field explicitly requests relative roughness.
- Use actual bore diameter. Scale and deposits can change both roughness and available flow area.
- For existing pipe, compare reasonable condition scenarios and use measured pressure/flow data where available. There is no universal age multiplier.
Example: 0.045 mm / 50 mm = 0.0009
1 in = 25.4 mm · 1 ft = 304.8 mm
In the usual fully developed laminar pipe model, Darcy f = 64/Re; roughness is not an input to that relation. Turbulent friction depends on Reynolds number and ε/D. A zero roughness entry represents the ideal smooth-wall limit, not frictionless flow.
Common mistakes
- Confusing ε with Hazen-Williams C, Manning n, or a dimensionless friction factor. These are different parameters.
- Using a surface finish Ra specification directly as hydraulic ε. They describe different aspects of the surface; obtain an appropriate hydraulic value.
- Using new-pipe values for corrosion, fouling, or heavy deposits without checking condition.
Pipe pressure drop · Darcy friction factor · Pipe network solver
Sources and scope
Pipe Flow Software: Pipe Roughness supplies the six material entries and concrete range used in the table and helper.
US EPA: EPANET 2.2 User Manual, Table 3.2 provides the independent new-pipe comparisons. Its Darcy-Weisbach column is in 10⁻³ ft: multiply the listed number by 0.3048 to obtain mm.
Sources checked September 28, 2026. Typical reference values are estimates, not material specifications or guaranteed design limits.