WATER PIPE SIZING

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This calculator helps you size domestic water piping using the velocity method, which is commonly used in Canadian practice as a quick check alongside the National Plumbing Code of Canada (NPC). You enter the design flow rate, select the water type (cold, hot, or custom), and specify a maximum design velocity in m/s. The tool then calculates the minimum internal diameter required to keep velocity at or below that limit and suggests an approximate trade size based on typical copper/PEX pipe IDs.

It also builds a small comparison table showing velocity for each nominal size (½", ¾", 1", etc.). At a glance, you can see which sizes would exceed your chosen velocity limit, which are acceptable, and which one is the first size that meets your velocity criteria. This makes it useful both for preliminary design and for sanity-checking an existing layout when you’re worried about noise, erosion, or excessive pressure loss from high velocities.

1. Enter the design flow rate
    
   • Type in the flow and choose the unit: L/min, L/s, or US gpm.
      
   • Use the probable peak demand for that section (not just a single fixture).
      

1. Select water type and maximum velocity
    
   • Choose Domestic cold water, Domestic hot water (< 60°C), or Custom.
      
   • The calculator will auto-fill a typical maximum velocity for cold or hot water (e.g., around 2.4 m/s for cold, 1.5 m/s for hot).
      
   • You can override this value if your AHJ, NPC amendments, or manufacturer recommends something different.
      

1. Review the results
   After clicking Calculate, you’ll see:
    
   • A converted design flow (showing equivalent L/min, L/s, and gpm).
      
   • The max design velocity you’re using.
      
   • The required minimum internal diameter in mm and inches.
      
   • A recommended trade size (first nominal size whose approximate ID is ≥ the required minimum).
      
   • Below that, the table lists each common trade size with:
      
   • Approximate internal diameter (mm)
      
   • Resulting velocity (m/s) at your design flow
      
   • A note such as “Too small”, “OK”, or “Recommended”
      

1. Apply engineering judgment & code checks
   Use the suggested size and velocity table as a starting point only. Final pipe sizing must still be checked against:
    
   • The National Plumbing Code of Canada (and any provincial/territorial amendments)
      
   • Local bylaws and AHJ requirements
      
   • Manufacturer data for the specific pipe material and SDR/series you are using
      

This tool is ideal for quick feasibility checks, early-stage design, and teaching apprentices how flow, velocity, and pipe size interact—while still respecting that final answers live in the NPC tables and manufacturer specs, not in a web calculator.