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Darcy-Weisbach Pipe Friction Head Loss Calculator

The Darcy-Weisbach equation universally quantifies frictional pressure head loss h_f along a straight pipe of length L and diameter D carrying fluid at velocity v with Moody friction factor f.

h_f = f × (L / D) × (v² / (2 × 9.80665))
Pick which value you want to calculate (or type into any field):Solving for: h_f — Frictional Head Loss
Calculated

Elevation head lost to pipe wall shear in meters of fluid

0.011,000.00

Dimensionless Moody friction factor (typically 0.012 – 0.040)

0.0050.1
unit

Total straight equivalent pipe run in meters

0.510,000.00

Inside diameter of pipe in meters

0.0055

Mean axial flow speed in m/s

0.130
Calculated Result · Frictional Head Loss (h_f)
4.0789m
Converted units:

Step-by-Step Calculation

01Canonical Law: h_f = f × (L / D) × (v² / (2 × 9.80665))
02Given Inputs (Base Units): f = 0.02, L = 100 m, D = 0.1 m, v = 2 m/s
03Solve for h_f (Frictional Head Loss): h_f = 4.0789 m

The Darcy-Weisbach equation universally quantifies frictional pressure head loss h_f along a straight pipe of length L and diameter D carrying fluid at velocity v with Moody friction factor f.

Real-World Reference Values

Smooth PVC / HDPE Pipef ≈ 0.013 – 0.018

Low relative roughness ε/D

Commercial Carbon Steelf ≈ 0.018 – 0.025

Absolute roughness ε ≈ 0.045 mm

Laminar Flow Exact Formulaf = 64 / Re

Valid when Reynolds number Re < 2,300

20-Row Comparison Table

Frictional Head Loss (h_f) · Darcy Friction Factor (f)

Darcy-Weisbach Pipe Friction Head Loss Calculator — Darcy Friction Factor → Frictional Head Loss
#Darcy Friction Factor (f)Frictional Head Loss (m)Δ %
010.005 1.0197 m-75.00%
020.012632 2.5761 m-36.84%
030.02 Current4.0789 m0.00%
040.027895 5.6889 m+39.47%
050.035526 7.2454 m+77.63%
060.043158 8.8018 m+115.79%
070.050789 10.3582 m+153.95%
080.058421 11.9146 m+192.11%
090.066053 13.471 m+230.26%
100.073684 15.0274 m+268.42%
110.081316 16.5838 m+306.58%
120.088947 18.1402 m+344.74%
130.096579 19.6966 m+382.89%
140.104211 21.253 m+421.05%
150.111842 22.8094 m+459.21%
160.119474 24.3659 m+497.37%
170.127105 25.9223 m+535.53%
180.134737 27.4787 m+573.68%
190.142368 29.0351 m+611.84%
200.15 30.5915 m+650.00%
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Frequently Asked Questions

How do I convert head loss h_f (in meters) to pressure drop ΔP (in kPa)?+

Multiply head loss h_f by ρ × g (for water, 1 meter of head equals 9.807 kPa or 1.422 psi).

What is the difference between Darcy friction factor f and Fanning friction factor?+

The Darcy-Weisbach friction factor f is exactly 4 times the Fanning friction factor (f_Darcy = 4 × f_Fanning).

How do I account for elbows, tees, and valves?+

Add the equivalent pipe length (L_eq = K × D / f) of all fittings directly to Pipe Length L.