The outside diameter of nominal 3/4-inch PEX tubing is exactly 0.875 inches (22.2 mm), matching the OD of standard 3/4-inch copper pipe under the Copper Tube Size standard.
One wrong measurement at the supply house sends you back to the truck with a handful of fittings that don’t fit. The outside diameter of 3/4 PEX is the single number that determines every crimp ring, expansion ring, and fitting you buy — and it isn’t 3/4 of an inch. Whether you’re running a new trunk line or branching off an existing manifold, what the OD of 3/4 PEX actually is decides what connects to it. Here is the exact spec, why it matters, and what else you need to know before buying a single fitting.
What Does 3/4″ PEX Actually Measure?
PEX tubing uses the Copper Tube Size (CTS) standard, not nominal pipe size. That means a 3/4-inch PEX tube has the same outside diameter as 3/4-inch copper and CPVC pipe — 0.875 inches (22.2 mm). The “3/4” label refers to an approximate nominal diameter rather than a precise ID or OD measurement. This consistency lets you mix PEX, copper, and CPVC fittings on the same CTS sizing without guesswork, as long as you match the nominal size.
The inside diameter of 3/4 PEX is smaller than its copper counterpart because the plastic wall is thicker. A typical ID for standard SDR-11 3/4 PEX is 0.681 inches (17.3 mm), while copper pipe of the same nominal size has a wider interior. That difference matters for flow calculations, which is why plumbing codes treat PEX sizing as its own category.
3/4 PEX Outside Diameter: The Spec Sheet
Below is the full set of technical specifications for standard 3/4-inch PEX tubing used in residential and light commercial plumbing. Every number here applies to CTS-rated PEX meeting ASTM F876 and F877 standards.
| Specification | Measurement | Notes |
|---|---|---|
| Nominal Size | 3/4″ CTS | Copper Tube Size standard |
| Outside Diameter (OD) | 0.875″ (22.2 mm) | Matches 3/4″ copper pipe OD |
| Inside Diameter (ID) | 0.681″ (17.3 mm) | Standard SDR-11 wall thickness |
| Minimum Wall Thickness | 0.097″ (SDR-11) | Varies by standard (SDR-9: 0.132″) |
| Maximum Working Pressure | 160 PSI at 73°F | Typical for PEX-A (varies by grade) |
| Temperature Range | -47°F to 230°F | Lower limit at sustained high temp |
| Minimum Bend Radius | 7 inches | Centerline radius |
| Volume per 100 ft | 1.83 gallons | Use for pressure-drop calculations |
The PEX Universe technical specs page confirms these dimensions and adds that the minimum bending diameter measured center-to-center on a 180-degree turn is 14 inches.
What About the Inside Diameter and Wall Thickness?
The ID of 3/4 PEX is not a fixed number because wall thickness changes by SDR class. SDR-11, the most common residential standard, gives a wall thickness of 0.097 inches and an ID close to 0.681 inches. SDR-9 uses a thicker 0.132-inch wall, which drops the ID further. Most consumer-grade PEX tubing sold at home centers is SDR-11, but the manufacturer’s spec sheet is the only way to confirm what you are holding. VEVOR’s non-oxygen barrier 3/4 PEX, for example, lists an ID of 0.66 inches with a wall thickness of 0.10 inches, which still falls within the CTS tolerance range.
The practical consequence is simple: if you are calculating flow for a long trunk line, assume the conservative ID of 0.66 inches unless you verify otherwise. A quarter-inch difference in ID over a 100-foot run adds up in pressure drop.
Common Sizing Mistakes to Avoid
The most frequent error is assuming 3/4 PEX has a 3/4-inch inside diameter. It does not — that number refers to the nominal copper tube size, not any physical dimension of the plastic tube. The actual ID is roughly 0.681 inches, so fittings sized for 3/4 CTS PEX are built around a 0.875-inch OD. Trying to mate PEX to PVC or iron pipe by nominal size alone is the fastest way to a leak.
The second mistake is running 3/4 PEX all the way to individual fixtures. A 3/4 main line feeding a manifold is correct for volume, but dropping to 1/2 PEX at each branch keeps pressure predictable. Keep trunk lines at 3/4 and branch lines at 1/2 for a balanced system.
How to Choose the Right PEX for Your Job?
The PEX type you need depends entirely on the water temperature and whether oxygen can enter the system. Cold water lines can use non-oxygen barrier PEX (usually blue), while hot water and recirculating loops call for oxygen-barrier tubing (often red or white). PEX-A offers more flexibility and takes expansion fittings; PEX-B is stiffer and uses crimp or clamp rings. Both hold pressure within the same range when installed correctly, but your local plumbing code may mandate one type over the other.
| PEX Type | Best Application | Key Difference |
|---|---|---|
| PEX-A (Expansion) | Residential hot/cold, tight spaces | Most flexible; uses expansion rings |
| PEX-B (Crimp) | Standard residential plumbing | Slightly stiffer; uses crimp or clamp fittings |
| Non-Oxygen Barrier | Cold water only | Blue color; lower cost per foot |
| Oxygen Barrier | Hydronic heating, recirculating lines | Red or white; prevents corrosion in closed loops |
Badger Pipe and SharkBite both offer NSF-certified 3/4 PEX for potable water, while Apollo sells PEX-B through Home Depot in 10-foot lengths for smaller jobs. For a full comparison of available products and tested options, see our roundup of the best 3/4-inch PEX tubing with pricing and user feedback.
Getting the Right Fit for Your Plumbing Project
Every fitting, ring, and tool you buy starts with one number: 0.875 inches. That is the OD of 3/4 PEX, and it determines whether a 3/4 CTS crimp ring slides on clean or sits loose. Match the nominal size to your fittings, keep branch lines at 1/2 inch, and verify the SDR class if wall thickness matters for your flow calculation. The spec sheet from the manufacturer is the only source you should trust for the exact ID of the roll in your hand.
FAQs
What does CTS mean on PEX tubing?
CTS stands for Copper Tube Size, the standard that gives PEX the same outside diameter as copper and CPVC pipe of the same nominal size. A 3/4 CTS PEX tube has a 0.875-inch OD, matching 3/4 copper pipe, so fittings designed for copper work on PEX without adapters.
Can I use 3/4 PEX for a shower supply line?
You can, but it is usually oversized for a single fixture. A 3/4 line delivers more flow than a standard shower head needs, which can cause excessive pressure and waste water. Run 3/4 to the manifold and switch to 1/2 PEX for the branch supplying the shower.
Is 3/4 PEX the same diameter as 3/4 PVC?
No. PVC pipe uses nominal pipe size (NPS), where 3/4 refers to the approximate inside diameter. PEX uses CTS, where 3/4 refers to the nominal copper size and the OD is exactly 0.875 inches. The two are not directly interchangeable without transition fittings.
What is the difference between SDR-9 and SDR-11 PEX?
SDR-9 has a thicker wall (about 0.132 inches) and a smaller ID, making it suitable for higher pressure applications. SDR-11 has a thinner wall (about 0.097 inches) and a wider ID, which is the standard for most residential water supply lines. Check the manufacturer’s spec sheet before buying.
Does PEX-A or PEX-B have a different outside diameter?
No. Both PEX-A and PEX-B use the same CTS standard, so a 3/4 tube from either type has an OD of 0.875 inches. The difference between them is flexibility and fitting method, not outer dimension. Fittings and crimp rings are interchangeable between types as long as the nominal size matches.
References & Sources
- PEX Universe. “PEX Tubing Technical Specs” Comprehensive OD, ID, wall thickness, and bending radius data for CTS PEX.
- iFanBrass. “PEX Pipe Size Chart” Confirms 0.875″ OD for 3/4″ PEX with SDR-11 wall data.
- Badger Pipe. “NSF Certified Non-Barrier 3/4 PEX” Lists OD, ID, and ASTM/NSF certification for potable water use.
- Lowes. “SharkBite 3/4-in x 10-ft Blue PEX-A Expansion Pipe” Product specs and pressure rating for PEX-A tubing.