PEX Plumbing Pipe Sizing and Flow Chart

Quick reference for PEX pipe sizes, flow rates, and fixture unit calculations. Essential for DIYers planning residential plumbing projects.

PEX Pipe Size & Maximum Flow Rate
Pipe SizeMax Flow (GPM)Typical UseNotes
1/2"2-3 GPMSingle fixtureShort runs only (<25 ft ideal)
3/4"5-7 GPM2-3 fixtures, branch linesMost common for distribution
1"10-12 GPMMain trunk, whole houseFrom water heater to manifold
1-1/4"15+ GPMLarge homes, high demandCommercial or luxury residential
Fixture Flow Rate Requirements
FixtureFlow Rate (GPM)Recommended Size
Bathroom Sink/Lavatory1.5 GPM1/2"
Kitchen Sink2.2 GPM1/2"
Shower2.5 GPM1/2" (short run) or 3/4"
Bathtub4 GPM3/4"
Toilet2.5-3 GPM1/2"
Washing Machine3 GPM1/2" (short run) or 3/4"
Dishwasher2.5 GPM1/2"
Outdoor Hose Bib5-10 GPM3/4"
Impact of Run Length on Flow

Longer pipe runs increase friction loss, reducing water pressure and flow rate. Always size up for long runs.

Run Length1/2" PEX3/4" PEX1" PEX
0-25 feet✓ Good for single fixture✓ Excellent✓ Excellent
25-50 feet⚠ Reduced pressure✓ Good✓ Excellent
50-100 feet✗ Too small✓ Acceptable✓ Good
100+ feet✗ Not recommended⚠ Marginal✓ Recommended
System Design Guidelines

Trunk & Branch System (Traditional)

  • Main Trunk: 3/4" or 1" from water heater
  • Branch Lines: 3/4" to bathroom/kitchen groups
  • Individual Drops: 1/2" to each fixture
  • Pros: Uses less pipe, familiar to plumbers
  • Cons: Pressure drops when multiple fixtures used simultaneously

Home Run / Manifold System (Modern PEX)

  • Setup: Central manifold with dedicated 1/2" line to each fixture
  • Main Feed: 3/4" or 1" from water heater to manifold
  • Pros: Better pressure at each fixture, easier shutoffs, less fittings
  • Cons: Uses more pipe, requires manifold installation
  • Best For: New construction, remodels with open walls
Water Pressure Considerations

Incoming Pressure:

  • 40-60 PSI: Standard residential, size pipes appropriately
  • Below 40 PSI: Size up pipes, consider booster pump
  • Above 80 PSI: Install pressure reducer to protect fixtures

Factors Reducing Pressure:

  • Long pipe runs (friction loss)
  • Undersized pipes
  • Too many fittings (each elbow = 1-2 ft of pipe equivalent)
  • Height difference (lose ~0.5 PSI per foot of elevation)
  • Multiple fixtures running simultaneously
Sizing Rules of Thumb
  • Main Supply Line: Always use 3/4" minimum, 1" preferred for larger homes
  • Hot Water Recirculation: Use 3/4" loop for best performance
  • Bathroom Group: 3/4" supply to bathroom, then 1/2" drops to individual fixtures
  • Kitchen: 3/4" supply, then 1/2" to sink and dishwasher
  • Laundry: 3/4" supply, can use 1/2" drops if runs are short (<15 ft)
  • When in Doubt: Size up - larger pipe ensures better pressure with minimal cost increase
  • Multi-Story Homes: Use 1" main trunk to upper floors to overcome elevation loss
Common Sizing Mistakes to Avoid

❌ Using 1/2" PEX for all runs to save money

Results in poor pressure when multiple fixtures are used

❌ Not accounting for run length

Long 1/2" runs (50+ ft) will have terrible pressure

❌ Undersizing the main trunk line

Bottleneck at source limits entire system

❌ Not considering simultaneous fixture use

Master bathroom with shower + toilet needs adequate branch sizing

PEX Type Comparison
TypeFeaturesBest For
PEX-AMost flexible, expandable fittings, best cold weatherPremium installs, freeze-prone areas
PEX-BGood flexibility, crimp/clamp fittings, economicalMost residential applications
PEX-CStiffest, least expensiveBudget projects, short runs

Note: All types have same internal diameter and flow characteristics

Additional Information

About This PEX Plumbing Sizing Guide

This comprehensive PEX plumbing pipe sizing guide helps DIYers and plumbers select the correct pipe diameter for optimal water flow and pressure throughout residential plumbing systems. Proper pipe sizing is critical for avoiding low water pressure, ensuring adequate flow to multiple fixtures simultaneously, and meeting plumbing code requirements.

PEX (cross-linked polyethylene) tubing has become the most popular choice for residential water supply systems due to its flexibility, corrosion resistance, and ease of installation. However, its flexibility and friction characteristics mean that pipe sizing is even more important than with traditional copper or CPVC piping. This guide covers flow rates for different pipe sizes, fixture requirements, the impact of run length on pressure drop, and design guidelines for both trunk-and-branch and manifold systems.

Whether you're replumbing an entire house or adding a single fixture, proper sizing ensures you'll have strong, consistent water pressure at every faucet and showerhead. Undersizing pipes is one of the most common DIY plumbing mistakes and results in frustrating low pressure that's expensive to fix later.

Why Use This PEX Sizing Reference Guide?

Correct pipe sizing ensures adequate water pressure and flow throughout your home. This guide helps you avoid the frustration and expense of undersized plumbing.

  • Determine the right pipe size for any fixture based on flow requirements
  • Account for run length when sizing pipes to prevent pressure loss
  • Design efficient trunk-and-branch or manifold plumbing systems
  • Understand how multiple simultaneous fixtures affect sizing needs
  • Compare PEX types (A, B, C) for your specific application
  • Avoid common sizing mistakes that result in poor water pressure
Frequently Asked Questions

Free PEX Plumbing Sizing Chart - Simple Flow Rate Guide | DIYProject.ai