Does roughness matter as much in laminar flow as in turbulent flow?

No — in laminar flow, friction factor depends only on Reynolds number (f = 64/Re) and is completely independent of pipe roughness, since the flow is smooth and orderly enough that surface irregularities don't meaningfully disturb it. Roughness only becomes a relevant input once flow is turbulent.

Should I always use the maximum roughness value in a material's typical range to be conservative?

Not necessarily — using an unrealistically high roughness value overstates pressure drop and can lead to oversized pumps or piping, which has its own cost. A more defensible approach is selecting a roughness value appropriate to the specific service condition and expected pipe age, informed by the actual fluid chemistry and service history where available, rather than defaulting to an extreme value in either direction.

Do internal pipe linings or coatings change the roughness value used in calculations?

Yes — a pipe with a smooth internal lining (such as cement mortar lining in some water pipes, or epoxy coatings) has a different effective roughness than the base pipe material alone, and the lining's roughness characteristics (new and aged) should be used instead of the unlined base material's typical values.

Engineering·6 min read·August 14, 2026

🧱 Pipe Roughness Values by Material: What to Use and Why

Typical absolute roughness values for common pipe materials, why roughness changes with pipe age and scaling, and how to choose a defensible roughness value for a pressure drop calculation.

By EngineersUniverse Editorial Team

Engineering Editorial & Technical Review Team

Published August 14, 2026

Why Roughness Is a Physical Input, Not a Universal Constant

Absolute pipe roughness (ε), the input that feeds directly into the friction-factor calculation for turbulent flow, is a property of the pipe's interior surface — specifically, a statistical measure of the height of surface irregularities relative to the mean surface. Unlike density or viscosity (which are fluid properties, independent of the pipe), roughness depends entirely on the pipe material, manufacturing process, and — critically — the pipe's service history, so choosing a defensible roughness value requires understanding what's actually being modeled, not just looking up a single generic number.

Typical Roughness Values by Material

Commonly cited absolute roughness values (in meters, for new/clean pipe) include: drawn tubing and glass, approximately 0.0000015 m (essentially hydraulically smooth); commercial/welded steel, approximately 0.000045 m; galvanized iron, approximately 0.00015 m; cast iron, approximately 0.00026 m; and concrete, a wide range from approximately 0.0003 to 0.003 m depending on the finish and construction method. These values span roughly three orders of magnitude across common materials — the choice of material genuinely changes the friction factor and resulting pressure drop meaningfully, not just marginally.

Why Roughness Increases With Pipe Age

The roughness values above describe new, clean pipe — in service, pipes accumulate scale, corrosion products, and biological growth (especially in water systems) on their interior surface, which increases effective roughness over time. This is why the same nominal pipe material can have a meaningfully higher effective roughness after years of service compared to its as-installed condition, and why prudent engineering practice for long-lived piping systems applies a margin above the "new pipe" roughness value rather than designing exactly to the clean-pipe number.

How Much Margin Is Appropriate

There's no single universal aging factor — the degree of roughness increase depends on the specific fluid service (corrosive or scaling fluids increase roughness faster than clean, non-reactive fluids), water chemistry (for water systems, hardness and dissolved mineral content strongly affect scale buildup rate), and whether the system includes corrosion-inhibiting treatment. Some engineering references suggest designing with roughness values several times the new-pipe value for systems expected to see significant scaling over their service life, while systems with well-controlled fluid chemistry or protective linings may see roughness increase much more slowly.

Smooth Pipe as the Practical Zero Case

Smooth plastic pipe (PVC, HDPE, and similar materials) has such low absolute roughness that it's often treated as effectively zero for practical calculation purposes — the friction factor in this case approaches the "hydraulically smooth" limit of the friction factor curve, where relative roughness has essentially no influence and friction factor depends on Reynolds number alone (the leftmost curve on a Moody chart). This is one reason plastic piping is often favored where minimizing frictional pressure drop matters, beyond its corrosion-resistance advantages.

Choosing a Value for a Real Calculation

For a preliminary or educational calculation, using a representative new-pipe value for the specified material (as this calculator's default of 0.000045 m for commercial steel does) is a reasonable starting point. For a real design calculation intended to support equipment purchase or piping specification, roughness should be selected based on the specific fluid service, expected pipe age at time of peak flow requirement, and any available plant-specific historical data on scaling behavior in similar service — not just a generic textbook table value applied without consideration of the actual operating context.

Topics covered

pipe roughness valuesabsolute roughness pipe materialcommercial steel pipe roughnesspipe scaling roughness