Pipe Sizing Calculator
For a 1.5 L/s water flow at 60 °C in copper pipe, DN32 gives 1.85 m/s velocity and 245 Pa/m pressure drop. Enter your flow rate, fluid and pipe material below to get a full pipe size comparison with velocity, pressure drop and Reynolds number.
This tool evaluates every standard DN size from DN15 to DN100, calculates Darcy-Weisbach pressure drop and Reynolds number for each, and recommends the optimal size based on your velocity and pressure drop limits.
Pipe Sizing Inputs
Recommended Pipe Size
Pipe Size Comparison
| DN | ID (mm) | Velocity (m/s) | Re | Flow Regime | ΔP (Pa/m) | Total ΔP (kPa) | Status |
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Pipe Sizing Formulas
Velocity from flow rate:
Reynolds number:
Darcy friction factor (Blasius, turbulent):
Darcy friction factor (laminar):
Darcy-Weisbach pressure drop:
Frequently Asked Questions
What is the recommended pipe velocity for water systems?
For closed-loop hydronic systems the recommended velocity is 1.0 to 1.5 m/s. Below 0.5 m/s air entrainment is a risk; above 3 m/s noise and erosion become concerns. Steam systems typically run at 15 to 25 m/s for dry steam.
How do I calculate pressure drop in a pipe?
Use the Darcy-Weisbach equation. For turbulent flow in smooth pipes, the Blasius approximation gives friction factor f = 0.316 / Re^0.25. Pressure drop per metre = f / D * (rho / 2) * v squared. This calculator automates the full computation.
What is Reynolds number and why does it matter?
Reynolds number predicts flow regime. Below 2,300 flow is laminar (smooth, low pressure drop). Above 4,000 it is turbulent (mixed, higher pressure drop but better heat transfer). The transition zone between 2,300 and 4,000 is unpredictable.
How does fluid temperature affect pipe sizing?
Temperature changes density and viscosity. Hot water at 80 °C has about one third the viscosity of 20 °C water, giving higher Reynolds numbers and different friction factors at the same flow rate. Always use operating temperature for accurate sizing.
Need Help Sizing Your System?
Our engineers can design complete hydronic systems for heat pump installations, including pipe sizing, pump selection and balancing.
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