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Pipe Friction Loss Calculator

Calculate pressure drop, head loss, velocity, and friction factor for pipe flow using Darcy-Weisbach (Colebrook-White) or Hazen-Williams.

Pipe & Flow
Fluid Properties
Density:998.21 kg/m³
Dynamic Viscosity:1.002 cP
Fittings (Equivalent Length)Show
Results
Pressure Drop
1.4931
Head Loss
0.15252
Velocity
0.3537
Reynolds Number
35243
Friction Factor (f)
0.023915
Flow Regime
Turbulent
Understanding Pipe Friction Loss

Friction loss is the pressure drop caused by fluid flowing through a pipe. It depends on the pipe diameter, length, internal roughness, flow velocity, and the fluid's density and viscosity. Accurately calculating friction loss is essential for sizing pumps, selecting pipe diameters, and ensuring adequate pressure at downstream equipment.

Darcy-Weisbach Method

The Darcy-Weisbach equation is the most general and theoretically rigorous approach to calculating friction losses. It works for any Newtonian fluid (water, oil, gas, refrigerants), any flow regime (laminar, transitional, turbulent), and any pipe size.

hf=f⋅LD⋅V22gh_f = f \cdot \frac{L}{D} \cdot \frac{V^2}{2g}
  • hfh_f — head loss due to friction (m)
  • ff — Darcy friction factor (from Colebrook-White equation)
  • LL — pipe length
  • DD — internal diameter
  • VV — flow velocity
  • gg — gravitational acceleration

The friction factor f is determined iteratively using the Colebrook-White equation, which relates f to the Reynolds number and the pipe's relative roughness (ε/D). This calculator solves it automatically.

Hazen-Williams Method

The Hazen-Williams formula is an empirical equation widely used in water distribution system design. It replaces viscosity and roughness with a single C-factor (roughness coefficient), making it simpler but less general.

hf=10.67⋅L⋅Q1.852C1.852⋅D4.8704h_f = \frac{10.67 \cdot L \cdot Q^{1.852}}{C^{1.852} \cdot D^{4.8704}}
  • hfh_f — head loss due to friction (m)
  • CC — Hazen-Williams coefficient (typically 100-150)
  • QQ — volumetric flow rate
  • DD — internal diameter
  • LL — pipe length

Hazen-Williams is only reliable for water near room temperature (5-25 °C) in turbulent flow through pipes larger than about 50 mm. It cannot be used for gases, oils, or refrigerants.

Which Method Should You Use?

Darcy-Weisbach is recommended as the default for general-purpose engineering calculations. It is more accurate and applicable to all fluids and flow conditions.

Hazen-Williams is appropriate when designing municipal water distribution networks, importing EPANET models, or when project specifications reference C-factors directly.

For a deeper comparison, see our blog post: Darcy-Weisbach vs Hazen-Williams.

Fittings and Equivalent Length

Pipe fittings (elbows, tees, valves, reducers) create additional pressure losses beyond straight-pipe friction. This calculator uses the equivalent length method (Crane TP-410 L/D ratios) to express each fitting as an equivalent length of straight pipe, which is then added to the total pipe length for the friction calculation.

Frequently Asked Questions

What is the difference between Darcy-Weisbach and Hazen-Williams?
Darcy-Weisbach is a general-purpose equation that works for any Newtonian fluid and any flow regime. It uses pipe roughness and the Colebrook-White friction factor. Hazen-Williams is an empirical formula limited to water (or similar liquids) in turbulent flow, using a dimensionless C-factor. Darcy-Weisbach is more accurate but requires fluid viscosity; Hazen-Williams is simpler and widely used in water distribution design.
What pipe roughness value should I use?
Roughness depends on material and condition. Typical values: commercial steel 0.045 mm, stainless steel 0.015 mm, copper 0.0015 mm, PVC/HDPE 0.0015 mm, cast iron 0.26 mm, concrete 0.3-3 mm. Aged or corroded pipes have higher roughness. When in doubt, use manufacturer data or err on the high side for conservative pressure drop estimates.
How do I account for fittings and valves in friction loss?
Fittings are commonly represented as equivalent lengths of straight pipe (L/D method from Crane TP-410). For example, a standard 90-degree elbow is roughly 30 pipe diameters of equivalent length. This calculator includes a fitting equivalent length input that adds to the straight pipe length before computing total friction loss.
What is the difference between gauge and absolute pressure?
Gauge pressure is measured relative to atmospheric pressure (0 psig = 1 atm). Absolute pressure includes atmospheric pressure (0 psia = perfect vacuum). For friction loss calculations the pressure drop (delta P) is the same in both systems, but inlet/outlet pressures must be consistent. This calculator reports pressure drop, which is independent of the reference.
Can I use this calculator for gas or steam piping?
Yes, for moderate pressure drops (under about 10% of inlet pressure) the incompressible Darcy-Weisbach equation gives reasonable results for gases. For larger pressure drops or compressible flow, you need a compressible flow equation that accounts for gas expansion along the pipe. SimuPipe's simulation engine includes an isothermal compressible solver for these cases.

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