Water Pipe Sizing Calculator (BS EN 806 & CIBSE Guide G)
Calculate required internal diameter, select certified commercial pipe dimensions, and evaluate pressure gradient and acoustic limits for potable water installations.
1
Design Parameters
Simultaneous maximum demand or peak design flow.
Recommended: 1.0 - 1.5 m/s
m/s
Roughness: ε = 0.0015 mm (Smooth drawn tube)
m
°C
90° Standard Elbows (K=0.75):
Standard Tees Through Branch (K=1.5):
Full-Bore Ball Valves (K=0.05):
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)