Pressure Drop Calculator

Friction Factor (f)

Moody diagram or use friction correlations

Pipe Diameter

Pipe Length

Fluid Velocity

Fluid Density

Gravitational Acceleration

Standard: 9.81 m/s²

Pressure Drop (Darcy-Weisbach)

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Note: This calculator uses the Darcy-Weisbach equation for major pressure losses. Minor losses (fittings, valves, bends) should be added separately as K × (ρV²/2). For rough pipes, use Colebrook-White or Swamee-Jain equations to determine friction factor.

Quick Friction Factor Lookup

Pipe Material	Condition	Roughness (ε, mm)	Typical f (Re=100k)
Commercial steel	New	0.045	0.020
Commercial steel	Corroded	0.15-0.25	0.030-0.035
Galvanized iron	New	0.15	0.025
Cast iron	Aged	0.25-0.8	0.035-0.045
Concrete	New	0.3-0.8	0.030-0.035
PVC/Plastic	New	0.0015	0.012-0.014
Glass	New	0.0015	0.008-0.010

Equations & Definitions

Darcy-Weisbach Equation

ΔP = f × (L/D) × (ρV²/2)

ΔP = Pressure drop (Pa)
f = Darcy friction factor (dimensionless)
L = Pipe length (m)
D = Pipe diameter (m)
ρ = Fluid density (kg/m³)
V = Velocity (m/s)

Colebrook-White Equation (Implicit)

1/√f = -2 log₁₀(ε/(3.7D) + 2.51/(Re√f))

Used for turbulent flow (Re > 4000)
ε = Absolute roughness (m)
Re = Reynolds number (dimensionless)

Swamee-Jain Equation (Explicit)

f = 0.25 / [log₁₀(ε/(3.7D) + 5.74/Re^0.9)]²

Accurate for: 5000 < Re < 10⁸ and 10⁻⁶ < ε/D < 10⁻²
Easier to calculate than Colebrook-White (no iteration needed)

Reynolds Number

Re = (ρVD) / μ

μ = Dynamic viscosity (Pa·s)
Flow classification:
Re < 2300: Laminar
2300 < Re < 4000: Transitional
Re > 4000: Turbulent

Minor Losses (Fittings & Valves)

ΔP_minor = K × (ρV²/2)

K = Loss coefficient (depends on fitting type)
Typical K values:
90° Elbow: K ≈ 0.9
45° Elbow: K ≈ 0.4
Full-open gate valve: K ≈ 0.2
Check valve: K ≈ 2.0
T-junction: K ≈ 0.6-1.0