Pipe-material C-factor library — sources and aging
Hazen-Williams C and Darcy roughness ε for every common pipe material, with new and aged values, sources, and notes on how each ages in service.
Every pipe-flow calc starts with two material numbers: the Hazen-Williams roughness coefficient C (higher = smoother) and the Darcy absolute roughness ε in metres. They
describe the same physical thing (interior surface roughness) in different mathematical
frameworks. This page is the reference table behind the calculators, with the sources cited.
Why "new" and "aged" both matter
Pipe roughness is not a static property. Iron and steel pipes accumulate tubercles, scale, and biofilm; even copper develops a mineral film that detectably changes capacity over decades. The question for sizing isn't "what is C today?" but "what will C be at year 25 of service life?". For most municipal and industrial design, you size for aged conditions. For residential plumbing with PVC or PEX, the new value is fine for the design life of the building.
Where the numbers come from
- ASHRAE Handbook of Fundamentals (2021), Ch. 22 (Pipe Sizing). Authoritative for HVAC and chilled-water systems.
- AWWA M11 (steel) and M9 (concrete). The standards behind municipal water-main design — both new and aged values.
- Crane Technical Paper 410. Most-cited industry reference for pipe and fitting values; the Moody-derived absolute roughness numbers come from here.
- Cameron Hydraulic Data, 19th ed. Cross-checks for the L/D fitting equivalents.
- NIST IAPWS-IF97. Water density and viscosity — the temperature-dependent fluid properties drive the Reynolds number.
Library
| Material | Group | C (new) | C (aged) | ε [mm] | Notes | Source |
|---|---|---|---|---|---|---|
| PVC (smooth plastic) | Plastic | 150 | 145 | 0.0015 | Most common potable / irrigation material; very low roughness, ages well | ASHRAE 2021 Ch. 22; AWWA C900 |
| CPVC (hot-water plastic) | Plastic | 150 | 145 | 0.0015 | Same hydraulics as PVC, rated for hot domestic water (≤ 93 °C) | ASTM F441 |
| PEX (cross-linked polyethylene) | Plastic | 150 | 145 | 0.0070 | Common residential hydronic / domestic; slightly rougher than PVC | ASTM F876 |
| HDPE (high-density polyethylene) | Plastic | 150 | 140 | 0.0070 | Common municipal water main and irrigation; fused joints | AWWA C901 |
| Copper (new) | Copper | 140 | — | 0.0015 | Type L drawn copper, plumbing-standard; smooth ID | ASTM B88 |
| Copper (aged, with mineral deposit) | Copper | 130 | — | 0.0300 | Older potable systems with mineral build-up; capacity drops ~7% vs new | ASHRAE 2021 Ch. 22; AWWA M11 |
| Carbon steel (new, commercial) | Steel | 130 | — | 0.0460 | Black-iron commercial steel, schedule 40; standard ε = 0.046 mm | Moody (1944); Crane TP-410 |
| Carbon steel (aged, light tuberculation) | Steel | 100 | — | 0.5000 | 10–20 year old systems carrying treated water | AWWA M11; ASHRAE 2021 Ch. 22 |
| Galvanized iron | Iron | 120 | 95 | 0.1500 | Older potable distribution; zinc-coated steel, rougher than copper | Moody (1944); Crane TP-410 |
| Cast iron (new, asphalt-coated) | Iron | 130 | 100 | 0.2600 | Common older municipal main; coating affects roughness substantially | Moody (1944) |
| Cast iron (aged / unlined) | Iron | 90 | — | 1.0000 | Heavy tuberculation; expect significant capacity loss | AWWA M9 |
| Concrete (smooth, formed) | Concrete | 130 | — | 0.3000 | Steel-trowelled finish, large mains | AWWA M9 |
| Concrete (rough, cast) | Concrete | 110 | — | 2.0000 | Cast-in-place, no surface finishing | Moody (1944) |
| Stainless steel | Stainless | 140 | — | 0.0150 | Sanitary / pharmaceutical / food-grade systems | ASHRAE 2021 Ch. 22 |
| Ductile iron, cement-mortar lined | Iron | 140 | 130 | 0.1000 | AWWA standard for water-main systems; lining preserves capacity | AWWA C151 / C104 |
| PVC Schedule 80 | Plastic | 150 | 145 | 0.0015 | Heavier-wall PVC for industrial and elevated-pressure service; same ID hydraulics | ASTM D1785 |
| Fiberglass (FRP / GRP, epoxy lined) | Plastic | 150 | 150 | 0.0050 | Filament-wound composite; corrosion-immune, very smooth ID, common in chemical / desalination loops | AWWA M45 |
| Copper Type K (drawn, heavy wall) | Copper | 140 | — | 0.0015 | Heaviest-wall copper tube — buried service and high-temp distribution | ASTM B88 |
| Brass (drawn) | Specialty | 135 | 130 | 0.0015 | Sanitary fittings, instrument lines; ε similar to copper | Crane TP-410; ASTM B43 |
| Aluminum (drawn) | Specialty | 145 | 140 | 0.0015 | Compressed-air mains, refrigerant lines; very smooth ID, corrosion-resistant in air | Engineering Toolbox; ASTM B210 |
| Riveted steel (legacy) | Steel | 110 | 90 | 0.9000 | Pre-1950 large-diameter water mains; rivet heads dominate roughness | Moody (1944); AWWA M11 |
| Titanium (CP-2) | Specialty | 145 | — | 0.0015 | Marine + chemical service, seawater heat exchangers; smooth ID and corrosion-immune | ASTM B338 |
| Asbestos-cement (legacy) | Concrete | 140 | 130 | 0.0500 | Mid-20th-century distribution; legacy systems being replaced. Use only for capacity audits of existing AC mains | AWWA M14 |
| Lead (legacy service line) | Specialty | 135 | 120 | 0.0015 | Pre-1986 service lines. Smooth, but a public-health hazard — replacement is the right answer; included for capacity audits | EPA LCRR; Engineering Toolbox |
| Vitrified clay (sewer) | Concrete | 100 | 80 | 0.5000 | Gravity-sewer staple; rough joints, high-friction. Sized for partial-flow Manning, not pressure | ASTM C700 |
Picking C in practice
1. Plastic (PVC, CPVC, PEX, HDPE)
Use C = 150 for both new and aged design. Plastics don't tuberculate and they don't corrode; biofilm is the only roughness source and its effect is small. The aged C value (145) we list is conservative for very long runs in older systems.
2. Copper
Use C = 140 for new copper, C = 130 for systems older than ~15 years. The mineral-deposit film on the interior accumulates faster in hard water and at high temperatures. Erosion-corrosion at high velocities can roughen the surface further; if your design velocity is > 1.5 m/s in hot-water service, drop another 10 points.
3. Steel
C is tightly tied to internal coating. New black-iron steel (Schedule 40, commercial) is C = 130 / ε = 0.046 mm. Cement-mortar lined ductile iron stays close to copper-grade smoothness. Unlined steel pipe carrying treated water drops to C ≈ 100 within a decade or two; carrying untreated water it can fall to C = 85 with heavy tuberculation. AWWA M11 has the canonical curves.
4. Cast iron and ductile iron
Modern ductile iron with cement-mortar lining is excellent — C = 140 new, drops to ~130 over 50 years. Unlined cast iron is the worst common material: C = 130 new, but routinely measured at C = 90-100 in aged distribution mains. Capacity loss compounds when sediment accumulates in low spots.
5. Concrete
Surface finish dominates. Steel-trowelled smooth concrete: C = 130. Cast-in-place rough concrete: C = 110. Aging is mild compared to iron. Used mainly for very large mains.
Open the tools
- Hazen-Williams calculator — applies C live
- Darcy-Weisbach calculator — applies ε live, with override
- Methodology — the master reference list