Quick reference for PEX pipe sizes, flow rates, and fixture unit calculations. Essential for DIYers planning residential plumbing projects.
Quick answer
| PEX size | Flow and typical use |
|---|---|
| 1/2" | 2 to 3 GPM: one fixture (sink, toilet, shower) on runs under 25 ft |
| 3/4" | 5 to 7 GPM: branch lines serving 2 to 3 fixtures, or runs over 50 ft |
| 1" | 10 to 12 GPM: main supply and whole-house trunk |
Sizes are nominal (copper tube size). Long runs lose pressure, so size up past 25 ft.
Planning this project at home?
Get a step-by-step plan with materials for plumb fixtures with PEX: tools, a shopping list and the order to do it in.
Add the fixtures on this line, the run length, and how many run at once. It sizes the line from the flow table below.
3/4" PEX
5.5 GPM peak demand over 40 ft
| Nominal Size | Outside Diameter (OD) | Inside Diameter (ID) |
|---|---|---|
| 3/8" | 0.500" | 0.350" |
| 1/2" | 0.625" | 0.475" |
| 3/4" | 0.875" | 0.671" |
| 1" | 1.125" | 0.862" |
Dimensions per ASTM F876 (copper tube size PEX). The inside diameter is what the water actually sees, and it is smaller than copper of the same nominal size, which is why nominal 1/2" PEX flows less than 1/2" copper.
| Pipe Size | Max Flow (GPM) | Typical Use | Notes |
|---|---|---|---|
| 1/2" | 2-3 GPM | Single fixture | Short runs only (<25 ft ideal) |
| 3/4" | 5-7 GPM | 2-3 fixtures, branch lines | Most common for distribution |
| 1" | 10-12 GPM | Main trunk, whole house | From water heater to manifold |
| 1-1/4" | 15+ GPM | Large homes, high demand | Commercial or luxury residential |
| Fixture | Flow Rate (GPM) | Recommended Size |
|---|---|---|
| Bathroom Sink/Lavatory | 1.5 GPM | 1/2" |
| Kitchen Sink | 2.2 GPM | 1/2" |
| Shower | 2.5 GPM | 1/2" (short run) or 3/4" |
| Bathtub | 4 GPM | 3/4" |
| Toilet | 2.5-3 GPM | 1/2" |
| Washing Machine | 3 GPM | 1/2" (short run) or 3/4" |
| Dishwasher | 2.5 GPM | 1/2" |
| Outdoor Hose Bib | 5-10 GPM | 3/4" |
Use 1/2" PEX for runs under 25 ft, and 3/4" beyond that; a washer draws about 3 GPM, which sits at the top of what 1/2" comfortably delivers on a short run.
Use 3/4" minimum from the meter or water heater, and 1" for larger or multi-story homes; 1/2" is only for fixture drops, never for the main line.
Use 1/2" PEX for a run to a single fixture and 3/4" for anything that feeds two or more, plus the water heater. The 1/2 vs 3/4 PEX flow rate chart has the GPM each size carries and the pressure it costs, from the manufacturer’s tables.
Longer pipe runs increase friction loss, reducing water pressure and flow rate. Always size up for long runs.
| Run Length | 1/2" PEX | 3/4" PEX | 1" 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 |
Trunk & Branch System (Traditional)
Home Run / Manifold System (Modern PEX)
Incoming Pressure:
Factors Reducing Pressure:
❌ 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
| Type | Features | Best For |
|---|---|---|
| PEX-A | Most flexible, expandable fittings, best cold weather | Premium installs, freeze-prone areas |
| PEX-B | Good flexibility, crimp/clamp fittings, economical | Most residential applications |
| PEX-C | Stiffest, least expensive | Budget projects, short runs |
Note: All types have same internal diameter and flow characteristics
Short answer: run 1/2" PEX to a shower when the line is under about 25 feet, and 3/4" PEX for longer runs, rain heads, or body sprays.
| Fixture | PEX size | Typical flow |
|---|---|---|
| Shower (standard head) | 1/2" (3/4" over ~25 ft) | 2.0 to 2.5 GPM |
| Shower (rain head or body sprays) | 3/4" | 3 to 5+ GPM |
| Bathtub | 1/2" or 3/4" | 4 to 6 GPM |
| Bathroom sink | 3/8" or 1/2" | 1.0 to 1.5 GPM |
| Toilet | 3/8" or 1/2" | 1.5 to 3 GPM |
| Kitchen sink | 1/2" | 1.5 to 2.2 GPM |
| Water heater, main trunk | 3/4" or 1" | 6 to 12 GPM |
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.
Correct pipe sizing ensures adequate water pressure and flow throughout your home. This guide helps you avoid the frustration and expense of undersized plumbing.
Permit check
New or rerouted supply lines are usually permitted plumbing work.
Inspections: Supply rough-in with a pressure test, then Final
Job checklist
Ticks are saved in this browser. A project keeps them on every device.
Code changes
Model codes update every three years, and the parts that move this sheet are water supply fixture units, minimum pipe sizes and PEX approval rules. Leave an email and we will tell you when we update it for a new code cycle.
Local code notes for your county
Cities and counties amend IPC, UPC and IRC Chapter 29, and the amendments are what inspectors fail people on. Tell us where the job is and your project gets the notes that apply there.
Ask about your situation. Posting needs a free account, and your question carries over so you get an answer with your project in view. Questions we hear often get answered on this sheet.
The short answer: 1/2 in PEX for single fixtures on runs under about 25 ft, 3/4 in for the water heater, branch lines and long runs, and 1 in for a whole-house main. Once the pipe is sized, these pages cover the rest of the job.
GPM, velocity and pressure loss per 100 ft for 3/8 to 1 in PEX.
Go/no-go check that your crimp tool is calibrated before the wall closes.
Vent pipe diameter by fixture units and developed length.
Which hole saw clears each pipe size through studs and joists.
Supply, relief valve and venting sizes for a tank swap.
Supply line and drain sizes under the sink.
Flange, wax ring and supply line, step by step.
Washer box, standpipe and drain sizes.
Pipe types, fittings and the common sizes in one page.
GPM and temperature rise for the fixtures you run at once.
Pump GPM, horsepower and basin size for your basement.
The PEX chart and the other plumbing sheets in one download.
GPM from a pit test or your basement, total head, horsepower from pump curves, basin size and backup power
GPM from your fixtures and groundwater by ZIP, then gas BTU or electric kW, amps and breakers
Tank size by bedrooms, existing tank volume, drain field area by soil and your pumping schedule
Chart specifying minimum diameter and length limits for drain, waste, and vent pipes
Manufacturer flow rate, velocity and pressure loss per 100 ft for 3/8, 1/2, 3/4 and 1 inch PEX
Pipe sizes, fittings, codes, soldering techniques, and common repairs