Determining what size pipes you need for your project can be confusing. Many people assume pipe size is the outer diameter of the pipe—but “pipe size” actually refers to what is called “nominal diameter.”
Fittings can be just as confusing. Their inside diameters must be large enough to fit over the pipe's outside diameter. A half-inch plastic elbow, for example, has an outside diameter of about 1-1/4 inches.
Use this guide to help you find the pipe and fitting sizes you need for your next project. (For help with sizing PVC, download our PVC and CPVC Pipes and Fittings Size Guide.)
(All Measurements in Inches)
|Outside or Inside Diameter||Decimal Equivalent||Nominal Diameter||Typical Threads Per Inch|
Pipe and tubing are not measured the same way. Tubing is measured and named based on the actual outside diameter of the tube.
PEX, or Cross-Linked Polyethylene Tubing, is another technology fast becoming popular, and it is measured and named by inside diameter.
|Pipe vs. Tubing||Outside Diameter|
|1/2” size pipe||27/32”|
|1/2” size tubing||1/2”|
One of the most common thread types is National Pipe Thread (NPT). These come in male (NPT, MPT, or MNPT) and female (FPT or FNPT). These are usually tapered threads used in joining and sealing pipes.
Another common thread is National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM). These straight thread pipes are typically used for mechanical joints.
BSP thread form stands for British Standard Pipe. It is based on trade size rather than actual diameter.
To learn more about pipe thread types, download our Pipe Thread Definitions eZTip.
Select the plumbing application you need for your next project.
If you are still having trouble choosing pipe or fittings, contact our Customer Service Center at firstname.lastname@example.org or call 855-289-9676.