Pipe Flow Calculator
Enter the internal pipe diameter (mm), flow velocity (m/s) and the Hazen-Williams C value to estimate water-flow rate and head loss per 100 m for water-supply design.
Input Data
Results
At a glance:Water-pipe flow Q = A·v (A is the pipe cross-section, v is the velocity). Hazen-Williams head loss per 100 m: hf = 10.67·L·Q^1.852 / (C^1.852·d^4.87) (Q in L/s, d in m). Too high a velocity causes noise, water hammer and large losses; too low tends to scale. Hong Kong residential supply recommends 1–2 m/s. This calculator is an estimate; actual design must include local losses and elevation differences.
Formula
Flow = π(d/2)² × v
Head loss / 100 m = 10.67 × 100 × Q^1.852 / (C^1.852 × d_m^4.87)
$$Q = A v$$$$h_f = \frac{10.67\, L\, Q^{1.852}}{C^{1.852}\, d^{4.87}}$$How to Use
- Enter the internal diameter (mm).
- Enter the design velocity (m/s).
- Enter the pipe material C value.
- The tool outputs the flow rate and head loss per 100 m.
Case Studies
Residential cold-water branch
DN25, 1.5 m/s, C150.
Flow about 0.74 L/s; head loss about 1.9 m/100 m.
Main riser
DN50, 2.0 m/s, C150.
Flow about 3.9 L/s; head loss about 2.1 m/100 m.
FAQ
Why keep velocity below 2 m/s?
High velocity raises water-hammer and noise risk and pump energy; residential supply is usually controlled at 1–2 m/s.
What is the C value for?
C reflects pipe roughness and scaling: PVC is high (smooth), steel drops as it rusts; designers take a conservative value.
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References
Content review: Calculatorism Editorial Team. Results are for reference only; please refer to the relevant authorities for the official figures.