Before you can install your new pipes, you have to make sure that you are using the correct pipe size. Measuring your pipes for the first time may feel like a difficult task but is an important part of the process. Here we will share everything you need to know about how to measure your plumbing pipes and some tips on how to install them yourself.

How Can I Measure Plumbing Pipes?

Some piping materials will be measured differently but there are a couple of measurements you should be concerned about the most. These two main measurements are the Outside Diameter (OD) and the Nominal Pipe Size (NPS). Plumbers tend to worry the most about these two measurements.

When they are shopping or talking about pipe size, they will usually refer to the pipe’s NPS. The width of the outside of the pipe is the OD. Finding a pipe’s NPS can be done by cross-referencing the OD measurement with an ASME chart. NPS and OD are two separate measurements.

Learn What Size Pipe You Have

When you have your pipe in hand, you’ll be able to easily tell what the size of the pipe is. All plumbing pipes and fittings will have the pipe’s NPS printed or labeled on the side of it. Plastic piping will be printed on the side with the kind of plastic material it is made from, the thickness, and the size. Copper plumbing pipes will be labeled with what copper material it is.

How To Measure Your Plumbing Pipes

It is possible for you to measure your plumbing pipes yourself. Here we will go over three methods for getting your pipes measured. The charts below will come in handy when you need to take the OD measurement and convert it to the NPS.

Copper Pipe NPS Reference Chart

Copper Pipe Size Outside Diameter Pipe Circumference
1/2″ 5/8″ 2″
3/4″ 7/8″ 2-5/8″
1″ 1-1/8″ 3-1/4″
1-1/4″ 1-3/8″ 4-1/8″
1-1/2″ 1-5/8″ 5-1/8″
2″ 2-1/8″ 6-5/8″
3″ 3-1/8″ 9-3/4″
4″ 4-1/8″ 13″

PVC, ABS, CPVC, Brass, and Steel Pipe NPS Reference Chart

Plastic/Metal Pipe Size Outside Diameter Pipe Circumference
1/2″ 7/8″ 2-5/8″
3/4″ 1-1/8″ 3-1/4″
1″ 1-3/8″ 4-1/8″
1-1/4″ 1-5/8″ 5-1/4″
1-1/2″ 1-7/8″ 6″
2″ 2-3/8″ 7-1/2″
3″ 3-3/8″ 11″
4″ 4-3/8″ 14-1/8″

Direct Diameter Measurement

The direct diameter measurement of a plumbing pipe will give you the pipe’s OD and can be found if you have access to the open end of your pipe. If the pipe is installed, you will need to use a different method. Use a ruler or measuring tape and put it directly across the open end of the pipe. This will give you the pipe’s direct diameter measurement.

Outside Diameter Measurement

To find the pipe’s OD measurement you will need to have some calipers. Use the calipers and measure the outside of the pipe. This number is the OD of your plumbing pipe. This is a great option if the pipe has already been installed.

Circumference Measurement

If you want to try the method of measuring the circumference of your pipe, you’ll need to do a little math. But we’ll share the equation with you and walk you through all the steps.

  • Get a string or flexible tape and wrap it around the pipe.
  • Write down the measurements of the string or tape.
  • Divide that measurement by pi (pi=3.1415). This measurement will be the pipe’s diameter.
  • Use the charts provided to know the NPS of your plumbing pipe.

Installation Tips For Plumbing Pipes

Installing a single broken or old pipe yourself may save you from an expensive repair bill. But if the plumbing job is more difficult, have a licensed professional complete it for you. We’ll share with you some tips to install your water pipes on your own.

Work With PEX Pipes

PEX piping is a great material option if you are wanting to replace only a small area of plumbing. PEX is a plastic plumbing pipe that has many benefits. The installation when working with this material is a lot easier, it is easy to cut, requires simple fittings, is flexible, and less expensive than other materials.

Make Sure You Have The Correct Size Pipe

Pipe size is crucial in plumbing. Check your local codes to ensure that you have the correct size before beginning. Certain parts of your plumbing system will need very specific-sized pipes so don’t skip out on measuring them.

Use The Same Pipe Materials

Corrosion can happen when more than one kind of pipe material comes in contact with each other. Examine your current or old plumbing pipes to make sure you are using the same type of pipe material. More than one kind of plumbing pipe can be used together but you will need specific fittings to attach them.

Inspect Fittings

Pipe fittings are the components in your plumbing system that adhere two pipes to each other and redirect water. Inspecting your fittings will assure you that you have the correct ones for the pipe material you are using. This will prevent leaks from taking place.


Dry fitting your plumbing pipes will allow you to confirm that you have the correct size pipe that you need for the repair or replacement. Do this before you permanently glue or attach the pipe. This will ensure that your plumbing system flows properly.

The JW Heating and Air team are experienced with pipe replacement and installation. Give us a call today to schedule your plumbing pipe installation!

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