Pipe Pressure Drop & Friction Loss Calculator (Darcy-Weisbach)

Rigorous hydraulic resistance calculation modeling surface roughness, Reynolds number, fluid viscosity, straight run friction, and valve minor loss coefficients.

Design Parameters

Design Flow Rate (Q) *

Simultaneous maximum demand or peak design flow.

Target Velocity (v) Recommended: 1.0 - 1.5 m/s

m/s

Pipe Material & Standard

Roughness: ε = 0.0015 mm (Smooth drawn tube)

Pipe Run Length (L)

Water Operating Temperature

°C

Recommended Commercial Pipe Size

28 mm

BS EN 1057 Table X Half-Hard

Inner Diameter (ID) 26.20 mm

Outer Diameter (OD) 28.00 mm

Wall Thickness 0.90 mm

Minimum Req. ID 23.03 mm

Actual Velocity Optimal

1.39 m/s

Continuity: v = 4Q / (π·D²)

Total Pressure Drop Darcy-Weisbach

21.4 kPa

0.214 bar 3.10 psi

Total Head Loss 85.6 kPa/100m

2.18 m head

7.15 ft of water column

Fluid Mechanics & Friction Verification

Reynolds Number (Re) 36,320 Turbulent Flow

Friction Factor (f) 0.0229 Swamee-Jain

Water Density (ρ) 998.2 kg/m³ @ 20°C

Kinematic Viscosity 1.004 × 10⁻⁶ m²/s

1. Theoretical Internal Diameter via Continuity Equation:

D_req = sqrt(4 * 0.00075 / (π * 1.20)) = 0.02821 m = 28.21 mm

2. Actual Velocity in Selected Commercial Pipe:

v = 4 * 0.00075 / (π * 0.02620²) = 1.39 m/s

3. Reynolds Number Check:

Re = (1.39 * 0.02620) / (1.004e-6) = 36,320 (Turbulent Flow)

4. Darcy Friction Factor (Swamee-Jain):

f = 0.25 / [log10((0.0015/3.7/26.20) + (5.74 / 36320^0.9))]² = 0.0229

5. Darcy-Weisbach Friction Pressure Drop:

ΔP = 0.0229 * (25 / 0.0262) * (0.5 * 998.2 * 1.39²) = 21.4 kPa (0.214 bar)

UK & US Plumbing Standard Tool

Copper Pipe Sizing & Flow Capacity Calculator

Optimized for BS EN 1057 (Table X half-hard tube) and ASTM B88 (Types K, L, M). Enforces strict erosion-corrosion velocity limits per CIBSE Guide G and CIPHE guidelines.

Service Type & Temperature

Required Flow Rate (L/s)

Length of Run (m)

Standard UK Copper Sizes Comparison

Nominal Size	Internal Dia	Flow Velocity	Pressure Loss / 10m	Status

Darcy-Weisbach Formulation

Pipe Friction & Pressure Loss Calculator

Rigorous hydraulic resistance model factoring in surface roughness ε, kinematic viscosity ν, pipe run length, and valve resistance coefficients (K).

Pipe Inner Diameter (mm) e.g. 2" Sch 40 Steel = 52.5mm

Length of Straight Pipe (m)

Design Flow Rate (L/s)

Pressure Drop 18.6 kPa 0.186 bar / 2.70 psi

Friction Head Loss 1.90 m 6.23 ft of water

Hydraulic Gradient 31.0 kPa/100m Standard commercial range

Pipe Pressure Drop & Friction Loss Calculator (Darcy-Weisbach)

Design Parameters

Fluid Mechanics & Friction Verification

Copper Pipe Sizing & Flow Capacity Calculator

Standard UK Copper Sizes Comparison

Pipe Flow Rate & Discharge Calculator

Pipe Friction & Pressure Loss Calculator

Pipe Velocity & Erosion Limit Checker

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