Pipe Absolute Roughness (ε) — Darcy-Weisbach Reference
Absolute roughness ε sets the relative roughness ε/D for the Moody diagram and the friction factor f in hf = f·(L/D)·V²/(2g). Values below are for clean, new pipe unless noted. For aging water mains, design to an end-of-life (aged) roughness.
Absolute Roughness by Material
| Material | ε (mm) | ε (ft) |
|---|---|---|
| Drawn tubing, glass, brass, copper | 0.0015 | 0.000005 |
| PVC, HDPE, smooth plastic | 0.0015–0.007 | 0.000005–0.000023 |
| Commercial steel / wrought iron (new) | 0.045 | 0.00015 |
| Asphalted cast iron | 0.12 | 0.0004 |
| Galvanized iron | 0.15 | 0.0005 |
| Ductile iron, cement-mortar lined | 0.10–0.12 | 0.00033–0.0004 |
| Cast iron (uncoated, new) | 0.26 | 0.00085 |
| Wood stave | 0.18–0.9 | 0.0006–0.003 |
| Concrete (smooth to rough) | 0.3–3.0 | 0.001–0.01 |
| Riveted steel | 0.9–9.0 | 0.003–0.03 |
| Corrugated metal pipe (annular) | ~45 | ~0.15 |
| Aged / tuberculated steel or cast iron | 1.0–3.0 | 0.003–0.01 |
Friction Factor Equations (Turbulent, Re > 4000)
Colebrook-White (implicit, the Moody-diagram basis):
Swamee-Jain (explicit, ±1% over 4000 < Re < 108, 10−6 < ε/D < 10−2):
Laminar flow (Re < 2000), roughness irrelevant:
Sources: Moody, L.F. (1944), "Friction Factors for Pipe Flow," Trans. ASME. White, F.M., Fluid Mechanics, Table 6.1. Swamee, P.K. & Jain, A.K. (1976), J. Hydraulics Div., ASCE. Aged values: AWWA M11 / utility practice.
Related cheat sheets and tools
Use ε with the Darcy-Weisbach tool, add fitting losses from the minor loss K card, and check the Reynolds number to confirm the flow regime. For water-distribution work the Hazen-Williams C method is the common alternative. For modeling a full pressurized or stormwater network, see HydroComplete.