Straight Tee Size Guide How To Identify The Right Size For Your Piping System

Choosing the correct Straight Tee size is one of the most important steps in building an efficient, leak-free piping system. A mismatched tee can cause serious issues — from pressure loss and turbulence to premature pipe wear or leaks. In this guide, we’ll walk you through how to measure and identify the correct Straight Tee dimensions, how NPS (Nominal Pipe Size) and OD (Outside Diameter) relate, and provide a practical Straight Tee size chart for quick reference.

1.What Is a Straight Tee?

A Straight Tee, also known as an Equal Tee, is a T-shaped pipe fitting used to split or combine fluid flow. All three outlets (two on the main run and one on the branch) have equal diameters, making it ideal for systems that maintain uniform flow throughout.

Key functions of a Straight Tee:

Split or combine fluid flow without changing pipe diameter

Maintain balanced pressure in both directions

Offer compact and simple installation in linear systems

Common applications:

Residential plumbing (e.g., water distribution lines)

HVAC piping (balanced fluid or air distribution)

Industrial and food-grade pipelines

2.Straight Tee Size Fundamentals

Before selecting the right Straight Tee, it’s crucial to understand the three main parameters that define its size:

Nominal Pipe Size (NPS)

The standard system used to label pipe and fitting sizes in North America (e.g., ½”, 1”, 2”). It’s not the actual physical measurement — rather, a standardized size designation.

Example: A 1” NPS pipe actually has a 1.315” OD (outside diameter).

Outside Diameter (OD)

The actual external measurement across the circular section of the pipe. Straight Tees are matched based on this OD to ensure a perfect fit.

Schedule (Wall Thickness)

Indicates pipe wall thickness (e.g., Schedule 40, Schedule 80). Higher schedules withstand higher pressures and temperatures.

Example: Schedule 80 Straight Tees are used for high-pressure systems, while Schedule 40 fits most residential or light commercial use.

3.Step-by-Step: How to Select the Correct Straight Tee Size

Step 1: Measure the Pipe OD

Use a caliper or pipe gauge to measure your existing pipe’s Outside Diameter. Match it to the corresponding NPS size using a standard NPS-to-OD chart.

Metal pipes (steel, copper): Measure OD with a caliper; e.g., 1.315” OD = 1” NPS.

Plastic pipes (PVC, CPVC): Usually labeled with NPS and schedule, but double-check OD for accuracy.

New systems: Refer to design drawings or specifications to confirm NPS and schedule before purchase.

Step 2: Check Pressure and Temperature Ratings

Match the Straight Tee schedule to your system’s pressure and temperature requirements.

System Type	Recommended Schedule	Typical Pressure
Residential Plumbing	Schedule 40	Up to 150 PSI
Industrial Steam / Oil Lines	Schedule 80 or higher	300+ PSI
High-Temperature Fluids	Thick-wall carbon steel or stainless steel	Depends on material

Step 3: Match Connection Type

The type of pipe end determines what Straight Tee connection you need:

Connection Type	Fitment Rule	Example Use
Threaded Tee	Matches NPS (e.g., 2” NPS threaded pipe = 2” NPS threaded tee)	Plumbing & small-diameter piping
Welded Tee	Matches OD of the pipe	Industrial steel systems
Socketed Tee	Sized to OD (PVC/CPVC)	Plastic water systems

Step 4: Cross-Reference with a Straight Tee Size Chart

Once you have NPS, OD, and schedule, verify your selection using a Straight Tee size chart.

4.Straight Tee Size Chart (Common Sizes & Dimensions)

Nominal Pipe Size (NPS)	Outside Diameter (OD, inch)	Outside Diameter (OD, mm)	Common Schedules	Typical Applications
½”	0.840	21.3	40, 80	Home plumbing, sink lines
¾”	1.050	26.7	40, 80	Small appliances, water heaters
1”	1.315	33.4	40, 80, 120	HVAC, light industrial
1½”	1.900	48.3	40, 80, 120	Commercial plumbing
2”	2.375	60.3	40, 80, 160	Industrial pipelines
3”	3.500	88.9	40, 80, 160	Water and wastewater systems
4”	4.500	114.3	40, 80, 200	Cooling and process lines

Note: All dimensions follow ASME B36.10M standards. Always confirm manufacturer specifications before installation.

5.Common Mistakes to Avoid When Choosing Straight Tee Sizes

Confusing NPS with Actual OD
A 1” NPS pipe is not 1” OD. Always check OD-to-NPS conversion before ordering.

Ignoring Schedule Compatibility
Schedule 40 and 80 fittings are not interchangeable. Using mismatched schedules can cause leakage or fitting stress.

Using Adapters Unnecessarily
Don’t oversize a tee and reduce it with an adapter — it increases turbulence and leak points. Use a Reducing Tee if size transition is needed.

Wrong Connection Type
A threaded tee cannot be welded. Always confirm pipe end type (threaded, welded, socketed).

6.FAQ

Q1: How can I confirm the NPS if my pipe isn’t labeled?
Measure the Outside Diameter (OD) and match it using the chart above. For example, 2.375” OD corresponds to a 2” NPS pipe.

Q2: Do Straight Tee sizes differ between materials (steel, PVC, copper)?
NPS is standardized, but slight OD variations exist between materials. Always verify OD before fitting.

Q3: Should flow rate affect tee size selection?
As long as the tee matches your pipe’s NPS and schedule, it will support the designed flow. Flow rate affects pressure, not tee size.

Q4: Can I use a larger tee with an adapter?
Avoid it. Adapters cause unnecessary joints and flow disruption. If you need a smaller branch, use a Reducing Tee.

7.Conclusion

Selecting the correct Straight Tee size is about precision and compatibility. Always verify three key factors:

Pipe OD matches the tee

Schedule corresponds to system pressure

Connection type aligns with pipe ends

Using the Straight Tee size chart and sizing guide above ensures your piping system operates efficiently, safely, and with long-term reliability.

Contact our engineering team for professional guidance.