BL2.ru
Boosty
ENRU

Pipe Head Loss Calculator Online: Reynolds Number, Friction Factor

Enter the fluid, flow rate or velocity, diameter, length and pipe material. The calculator finds the Reynolds number and flow regime, the friction factor λ (Poiseuille, Blasius, Altshul, Colebrook), major and minor head losses, with a step-by-step solution and pipe sizing.

Water properties come from a table for t = 0…100 °C (linear interpolation); for another fluid enter ρ and ν (1 cSt = 1 mm²/s). Empty minor-loss fields count as zero. Enter an allowable loss H_max to size the diameter.
Calculate

How head loss is calculated

The total head loss in a pipeline is the sum of major (friction) and minor losses: H = hl + hm. Major loss follows Darcy–Weisbach: hl = λ·(L/d)·v²/(2g); minor loss is hm = Σζ·v²/(2g). Multiply by ρ·g to get the pressure drop: ΔP = ρ·g·H; 1 bar = 10⁵ Pa ≈ 10.2 m of water.

Reynolds number and flow regime

Re = v·d/ν is the ratio of inertial to viscous forces. For Re < 2300 the flow is laminar, for Re > 4000 fully turbulent, and in between lies an unstable transitional (critical) region. For water at 20 °C ν ≈ 1.0·10⁻⁶ m²/s, so in a 100 mm pipe the flow is turbulent from about 0.04 m/s — nearly all water pipes run turbulent.

Resistance zones

For turbulent flow the relative roughness ε = Δ/d is used. If Re < 10/ε the pipe is hydraulically smooth (λ depends on Re only); for 10/ε < Re < 500/ε the zone is mixed (depends on Re and ε); for Re > 500/ε it is fully rough (depends on ε only, loss proportional to v²).

Friction factor formulas

  • Poiseuille (laminar): λ = 64/Re;
  • Blasius (smooth pipes, 4000 < Re < 10⁵): λ = 0.3164/Re0.25;
  • Altshul (all turbulent zones): λ = 0.11·(Δ/d + 68/Re)0.25;
  • Colebrook–White: 1/√λ = −2·log₁₀(Δ/(3.7d) + 2.51/(Re·√λ)) — an implicit equation solved iteratively; it is the reference and underlies the Moody chart.

The calculator shows all four values and their deviation from Colebrook; Poiseuille is used for Re < 2300 and Colebrook otherwise.

Minor losses and roughness

The ζ coefficients depend on the fitting (elbow, tee, gate valve, globe valve, entrance and exit) and are tabulated in Idelchik; typical values are built in, and any others can be added in the field “Other”. Roughness Δ comes from the material table; for old pipes it is several times larger than for new ones.

Pipe sizing

Losses fall with diameter (roughly as d⁻⁵ at constant flow), so the diameter giving the allowable head loss is found numerically, then the next larger standard DN is chosen.

FAQ

How do I calculate head loss in a pipe?
Find the velocity v = 4Q/(πd²), the Reynolds number Re = vd/ν, the friction factor λ (from Re and Δ/d), then the major loss h = λ·(L/d)·v²/(2g) and add the minor losses Σζ·v²/(2g). The calculator does this step by step.
At what Reynolds number does flow become turbulent?
In round pipes the flow is laminar for Re < 2300 and turbulent for Re > 4000. In between is a transitional region where the regime is unstable and no reliable friction formulas exist.
Which friction formula should I use — Blasius, Altshul or Colebrook?
Blasius is only for smooth pipes up to Re = 10⁵. Altshul is simple and typically within a few percent of Colebrook in all zones. Colebrook–White is the most accurate but needs iteration; it is the one used here for turbulent flow.
How do I convert head loss to pressure and bar?
ΔP = ρ·g·H. For water 1 m of head loss ≈ 9.8 kPa ≈ 0.098 bar, that is 10 m of water ≈ 1 bar. The calculator reports m, Pa, kPa and bar.
How do I choose a pipe diameter from the allowable loss?
Enter the allowable loss H_max (the field at the bottom of the form): the calculator numerically finds the diameter with H = H_max and suggests the next standard DN. Remember that the real inner diameter differs slightly from DN.