What is the Pipe Flow Calculator?
Calculate pressurized pipe flow with this free pipe flow calculator. Find volumetric flow rate Q = A × v from diameter and velocity, solve mean velocity from flow rate, estimate friction head loss with the Darcy–Weisbach equation, or size water pipes with Hazen–Williams. Get Reynolds number, laminar/turbulent regime, pressure drop in kPa, and results in L/s, GPM, CFS, and m³/hr. PVC, steel, and cast iron C presets. Metric and imperial units. Runs instantly in your browser.
How to use the Pipe Flow Calculator
- Choose Flow Rate, Velocity, Darcy–Weisbach, or Hazen–Williams mode.
- Select metric or imperial units.
- Enter pipe internal diameter; add length, velocity, flow rate, head loss, or friction factor as required.
- Use Hazen C or Darcy f presets for common pipe materials.
- Review flow rate, velocity, head loss, pressure drop, Reynolds number, and copy results.
Common use cases
- Sizing a water supply line from diameter and target velocity
- Estimating friction head loss in a long pipeline run
- Checking if a PVC or steel pipe can carry required GPM
- Plumbing and fire-protection hydraulics homework
- Comparing Darcy vs Hazen–Williams for pump head calculations
Frequently asked questions
- What is the Darcy–Weisbach equation?
- Friction head loss h_f = f × (L/D) × v²/(2g), where f is the Darcy friction factor, L is pipe length, D is diameter, v is mean velocity, and g is gravity. Pressure drop ΔP = ρgh_f.
- What is Hazen–Williams used for?
- Hazen–Williams estimates flow velocity in full water pipes: v = 0.849 × C × R^0.63 × S^0.54 (SI units, R = D/4). C is a roughness coefficient — PVC ~150, new steel ~120, old cast iron ~80.
- How do I calculate flow rate in a pipe?
- For known diameter and velocity, Q = π(D/2)² × v. Use Flow Rate mode, or Velocity mode if you know Q and need v.
- What Reynolds number indicates turbulent flow?
- Re = vD/ν. Laminar flow is typically Re < 2,300; turbulent flow Re > 4,000. Water at 20°C uses ν ≈ 1.004×10⁻⁶ m²/s.
- How is this different from the water flow calculator?
- The water flow calculator covers open channels and Manning's equation. This pipe flow calculator focuses on pressurized pipes with Darcy–Weisbach head loss and Hazen–Williams sizing for water distribution.
