Plumbing Supply Pipe Sizing Calculator
Size main water supply and branch lines (Copper/PEX) based on Water Supply Fixture Units (WSFU) and peak flow rate GPM.
Input Parameters
Enter dimensions and specifications to estimate materials.
Recommended Main Supply Size
Branch Line Size
3/4" riser feeding 1/2" fixture branches
Total Fixture Units
20WSFU
Estimated Peak Demand
14GPM
Developed Length
80ft
System Summary
System accommodates 20 WSFU fixture load at ~14 GPM peak flow rate across 80ft pipe run.
Material estimates include recommended trade waste buffer. Always confirm dimensions on site prior to ordering.
How The Calculation Works
Formulas, material coverage assumptions, waste buffers, and rounding standards.
Fixtures are converted to Water Supply Fixture Units under the IPC/UPC method. WSFU is a demand weighting, not a count — it reflects the probability that fixtures run simultaneously, which is why ten fixtures do not need ten times one fixture's capacity.
Total WSFU is converted to peak demand in gallons per minute using the Hunter curve, then matched against pipe capacity at your supply pressure.
Developed length is the actual pipe run including every fitting, not the straight-line distance. Friction loss grows with length, so a long run may need the next size up at the same fixture count.
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Frequently Asked Questions
Practical installation guidance and purchasing tips for plumbing supply pipe sizing calculator.