Water Supply Pipe Sizing Calculator (WSFU)
Size PEX, Copper, and CPVC main service and branch lines using IPC & UPC Water Supply Fixture Units (WSFU) and Hunter's Curve.
Select Architecture Preset or Enter Custom Fixtures
Quickly load standard building templates verified against IPC Appendix E
1. Plumbing Fixture Schedule (WSFU)
Total: 25 WSFU2. Supply Pipe & Pressure Settings
About This Calculator & IPC Technical Methodology
Professional hydraulic calculation engine built to International Plumbing Code (IPC Table E103.3) and Uniform Plumbing Code (UPC Appendix A). Accurately aggregates fixture counts into Cold and Hot WSFU, converts demand into peak GPM via Modified Hunter's Curve, enforces the 8.0 fps water hammer velocity threshold, and sizes main lines and branch manifolds across PEX, Copper Type L, and CPVC.
Per the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), water supply pipe sizing must satisfy two simultaneous design constraints: (1) Total demand cannot cause fluid velocity to exceed 8.0 ft/s for cold water and 5.0 ft/s for hot water to prevent erosion-corrosion and water hammer, and (2) Frictional head loss through pipe walls and fittings, combined with static head loss of 0.433 PSI per vertical foot, must leave at least 15 to 20 PSI residual pressure at the highest fixture.
ToolHub Mechanical & Plumbing Group
Master Plumber & Certified Plumbing Designer (CPD) · ASSE Certified & ASPE Member
Strict compliance with IPC Table E103.3, UPC Appendix A, and ASPE Chapter 5 standards.
Frequently Asked Technical Questions
What is a Water Supply Fixture Unit (WSFU) and how is it used in pipe sizing?
A Water Supply Fixture Unit (WSFU) is an engineering measure of the probable water demand exerted by a single plumbing fixture (e.g. toilet = 2.5, shower = 2.0, kitchen sink = 1.5). Because not all fixtures run simultaneously, WSFU values are aggregated and converted into a diversified peak flow rate (Gallons Per Minute - GPM) via Hunter's Curve per IPC Table E103.3(2).
What is the maximum water velocity permitted in residential copper and PEX piping?
Per IPC Section 604.4 and copper development guidelines, cold water velocity must not exceed 8.0 feet per second (fps) to prevent turbulent erosion-corrosion and water hammer knocking. Hot water lines are limited to 5.0 fps. Excessive velocity strips the protective copper oxide patina and wears through PEX fittings prematurely.
Why does PEX require a larger trade size than Copper for the same flow rate?
PEX tubing (ASTM F876) has thicker pipe walls than standard Type L or Type M copper. For example, 3/4" PEX has an inside diameter of approximately 0.671 inches compared to 0.785 inches for 3/4" Type L Copper. Additionally, insert PEX crimp fittings restrict the internal diameter even further. Consequently, high-demand circuits may require 1" PEX where 3/4" Copper would suffice.
How do you calculate pressure loss over an elevated 2-story home?
Water exerts a hydrostatic head pressure of 0.433 PSI per vertical foot of elevation (1 PSI per 2.31 feet). For a second-floor bathroom elevated 15 feet above the street water meter, elevation loss alone deducts ~6.5 PSI (15 × 0.433) before accounting for friction loss through pipes, fittings, backflow valves, and water softeners.
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