What does the Pipe Flow Pressure Drop Calculator compute?

The calculator uses the Darcy-Weisbach equation ΔP = f·(L/D)·ρU²/2 to compute pressure loss ΔP (in Pa and bar), Darcy friction factor f, and Reynolds number Re in real time. For laminar flow (Re < 2300) it uses f = 64/Re; for turbulent flow (Re ≥ 4000) it iteratively solves the Colebrook-White equation; the transition region (2300 ≤ Re < 4000) uses linear interpolation.

How do I use the pipe flow calculator?

1. Set pipe diameter D (5–500 mm) and length L (0.1–1000 m) with the sliders. 2. Select pipe material roughness (steel 0.046 mm, cast iron 0.26 mm, glass/PE 0.0015 mm, concrete 1 mm) or enter a custom value. 3. Toggle between flow rate Q (m³/s) and velocity U (m/s) input. 4. Choose fluid (water 20°C, air 20°C, or custom ρ and μ). Results update instantly on the Moody chart and pressure drop curve.

What is the Moody chart and why is it important in pipe design?

The Moody chart is a log-log diagram plotting Darcy friction factor f against Reynolds number Re for various relative roughness values ε/D. It covers laminar, transition, and turbulent flow regimes in a single reference chart. In pipe system design it is used to quantify frictional head loss, size pumps, and calculate flow rates. In the fully turbulent rough-pipe regime (high Re), friction factor depends only on ε/D and is independent of Re.

How is the Colebrook-White equation solved?

The Colebrook-White equation 1/√f = −2 log(ε/(3.7D) + 2.51/(Re√f)) is implicit in f and is solved by fixed-point iteration starting from f = 0.02. The iteration converges to within 10⁻⁸ in about 5–10 steps. An explicit Swamee-Jain approximation (±2% error) is also widely used in hand calculations: f ≈ 0.25 / [log(ε/(3.7D) + 5.74/Re⁰·⁹)]².

Pipe Flow Pressure Drop Calculator (Moody Chart) — Free Online Calculator

Pipe Parameters

Diameter D 50 mm

5 mm500 mm

Length L 10.0 m

0.1 m1000 m

Roughness ε (Material)

Input by Flow Rate Q (OFF = Velocity U)

Flow Rate Q 0.010 m³/s

0.001 m³/s1 m³/s

Fluid

$Re = \rho U D / \mu$
$f_{lam} = 64/Re$
C-W: $1/\sqrt{f} = -2\log(\varepsilon/3.7D + 2.51/Re\sqrt{f})$
$\Delta P = f \cdot (L/D) \cdot \rho U^2/2$

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Reynolds Number Re

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Friction Factor f

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Pressure Drop ΔP (Pa)

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Pressure Drop ΔP (bar)

Pipe Flow Pressure Drop Calculator Moody Chart

Pipe Parameters

Moody Chart (f vs Re)

Pressure Drop ΔP vs Flow Rate Q