Engineering Tools
Pipe Sizing Calculator
Enter flow rate and design velocity to instantly calculate the required pipe diameter and recommended standard pipe size for chilled water, condenser water, or refrigerant piping. Suitable for HVAC water system piping design. Results are for preliminary reference only.
Pipe Diameter Calculation
Calculation Results
Calculation Formulas
This tool calculates pipe diameter based on design flow rate and velocity, suitable for preliminary HVAC water system piping design.
Flow rate unit conversion to m³/s:
LPM: Q = Q_lpm ÷ 60,000
CMH: Q = Q_cmh ÷ 3,600
GPM: Q = Q_gpm × 0.0000631
Calculated pipe diameter:
A = Q ÷ V (cross-sectional area, m²)
D = √(4 × A ÷ π) × 1000 (diameter, mm)
Where Q = flow rate (m³/s), V = velocity (m/s).
Standard pipe size selection:
The calculated diameter is matched against standard commercial pipe sizes (15mm ~ 400mm), selecting the nearest standard size equal to or larger than the calculated value.
Actual velocity:
Vactual = Q ÷ (π × (Dstd ÷ 1000)² ÷ 4)
Reynolds number (water at approx. 15°C):
Re = Vactual × (Dstd ÷ 1000) ÷ ν
Where ν = 1.14 × 10-6 m²/s (kinematic viscosity of water at 15°C). Re < 2,300 indicates laminar flow, 2,300~4,000 is transitional, and > 4,000 is turbulent flow.
Frequently Asked Questions
What are the design standards for chilled water pipe velocity?
Main chilled water pipes are recommended at 1.5~3.0 m/s, and branch pipes at 0.9~1.8 m/s. Excessively high velocity increases pipe noise and friction losses, while excessively low velocity results in oversized pipes and increased costs. Generally, 2.0~2.5 m/s is optimal.
Why do I need to select a standard pipe size after calculation?
Commercially available steel and copper pipes come in fixed standard sizes (e.g., 2", 3"). In engineering practice, you must select the nearest standard size that is equal to or larger than the calculated diameter to ensure flow requirements are met with adequate margin.
What is the Reynolds number and how does it relate to piping?
The Reynolds number (Re) determines whether flow is laminar (Re < 2,300) or turbulent (Re > 4,000). HVAC water systems typically operate in turbulent flow, which affects friction loss calculations differently. Larger pipe diameters and lower velocities result in smaller Reynolds numbers.
Professional Consultation
Need Professional HVAC Piping Engineering?
Online tools provide preliminary estimates for reference. Actual piping engineering design must account for pipe pressure losses, pump head, pipe material selection, and support/hanger systems. Contact our engineering team for precise HVAC system planning.