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How To Measure Pipe Size The Easy Way - Plumb University

How To Measure Pipe Size The Easy Way

by Trevor Woods | Last Updated: May 25, 2021

You’ve got a plumbing project on your hands and you need to know the size of your pipes.

Most people reach for a tape measure or ruler to measure their pipes, but this can lead to frustrating and inaccurate measurements. There are many factors involved in measuring pipe size and it can get even more confusing when calculating fractions – Ugh!

Don’t sweat it, we will get you measuring pipe like a pro in no time! Our free pipe wrap-around ruler is perfect for measuring the size of any type of plumbing pipe – including iron, PVC, copper, and more.

It’s so simple – just wrap it around your pipe and see what size of pipe you’re working with! Our handy dandy pipe measuring tool will help you get the job done quickly and easily!

The best part? It’s completely free and we will show you how to use it!

How Is Pipe Measured?

Plumbing pipes are measured differently depending on their type. The two measurements most plumbers are concerned about are Outside Diameter (OD) and Nominal Pipe Size (NPS).

The OD of a plumbing pipe is measured as the name implies is the width of the outside of the pipe. Whereas NPS takes the Outside Diameter of a pipe and crossreferences it with an ASME chart to get the “nominal size”.

This nominal size is what plumbers use when describing and shopping for pipes and fittings.

For example, tubing – like the soft copper you find in rolls, is measured by the Outside Diameter. The OD of copper tubing rounded to the nearest 1/8th of an inch for accuracy.

The misleading part is that tubing Outside Diameter measurement is not the Nominal Pipe Size – confusing right? This creates perplexing plumbing problems when trying to measure pipe size.

Copper Pipe SizeOutside DiameterPipe Circumference

How Do You Know What Size Pipe You Have?

Plumbing pipes and fittings are marked with their Nominal Pipe Size. Copper pipe for instance will be labelled to indicate the NPS as well as the type of copper pipe it is. Plastic pipes also have their specifications printed on them to let you know what kind of plastic it is, the size, and even pipe wall thickness.

If you can’t see with your peepers what size of pipe you are looking at there are a few ways to measure your plumbing.

How Do I Measure My Pipe Size?

There are a few ways to measure pipe size, and we will save the best for last! With each means of measuring your pipe, you will need these charts to convert your Outside Diameter measurement into Nominal Pipe Size.

Copper Pipe NPS Reference Chart

Copper Pipe SizeOutside DiameterPipe Circumference

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

Plastic/Metal Pipe SizeOutside DiameterPipe Circumference

Direct Diameter Measurement

The simplest way to measure your pipe’s outside diameter is across the end of the pipe itself with a measuring tape or ruler.

The downside of this technique is that you need access to an open end of a pipe to measure across. If your plumbing pipe is already installed, it might be impossible to measure your pipe this way.

Outside Diameter Measurement

This method is handy if you can’t measure from an open end of a plumbing pipe. A set of callipers can be used to quickly take an accurate measurement of your pipe’s diameter.

Circumference Measurement

Another way to measure pipe size is to measure the pipe’s circumference, convert that measurement into a diameter, and then reference its Nominal Pipe Size.

Sounds complicated – right? But it’s very simple math and we have the equation for you so you can calculate pipe size with ease!

All you need to do is wrap a string or a flexible tape measure around the outside of the pipe. Now, take this measurement and divide it by pi (pi = 3.1415). This calculation is the plumbing pipe’s Outside Diameter that you can use to look up the Nominal Size.

For instance, let’s say you wrapped your lucky shoelace around the pipe and marked the circumference on the shoelace. Comparing your shoelace to a measuring tape, you found the length of the string circumference is almost 7-1/2″.

7-1/2″ ÷ pi (or 3.1415) = 2.38″ Outside Diameter.

An OD of 2.38″ is a 2″ Nominal Pipe Size.

What’s The Easiest Way To Measure Pipe Size?

What if you don’t own a set of callipers or math was your most hated subject in school? We hear you!

That’s why we created a pipe wrap-around measuring tool. Easy to use, no math required, and the best part is it’s free!

Plumb University Pipe Ruler

The perfect tool for anyone needing to measure pipes!

Take the guesswork out of your plumbing project with our easy-to-use ruler, and quickly see the size of your pipe instantly!

Simply wrap the ruler around your plumbing pipe and see how it measures up!

Download Now

How Do I Use The Pipe Measuring Tool?

Simply download our free pipe size measuring tape and print it off. Next, cut out the pipe size ruler and wrap it around the pipe you want to measure.

The pipe measuring tape is marked with Nominal Pipe Sizes so you can quickly see the size of pipe you have. You can also double-check your measurements with the pipe size charts that come with our wrap-around ruler. Done!

Does Pipe Measuring Tool Work On All Kinds Of Pipe?

You bet! Our pipe measuring tool works on brass, steel, copper, and plastic pipes like PVC, ABS, and CPVC. This pipe measuring tape has you covered for all the common kinds of pipe you’ll find in your home!

How Do Your Pipes Measure Up?

Don’t sweat another inaccurate measurement or plumbing math problem again! We’ve shown you how to take all the guesswork out of measuring your pipe size.

And if you want, you can impress your friends with your new nifty pipe measuring tool!

Happy Plumbing!

Trevor Woods is the founder of Plumb University® and he started in the plumbing and construction industry in 1997. Since then, his mission is to make plumbing repair and maintenance easy for everyone. And each year, he continues to help more people with their plumbing installation, care, and troubleshooting.