Close this search box.

How To Measure Copper Pipe in No Time

You must know some basics about pipes and plumbing in those events. And it’s time we lay down some ground rules: Always take measurements of the pipes before opening your water line.
Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Knowing your pipe measurements can make your task very easy, and you can focus on the plumbing part and not the sizing part.

This article will show and teach you how to measure a copper pipe. Well, measuring pipes is easy once you know what you are supposed to do. However, the problem arises with the confusion of measuring a tube and a pipe.

People often get lost at the ID and OD part of the measurement (we will discuss it later in this article). For now, let’s start with the basics and clear out the confusion you may have about copper pipes.

Measuring A Pipe 101

Measuring A Pipe 101

When you measure a pipe from the inside, it is called a nominal diameter, unlike the standard diameter, where you measure outside.

NPS or Nominal Pipe Size is a North American standard-size set for the pipe. It also takes into account a wall thickness which is called its Schedule. One thing that is and will always remain true is the size.

The outside of the pipe is always larger than the inside. Therefore, a pipe is always measured from the inside. If you do not have the required set of tools to measure the size from the inside, you can follow the string method demonstrated in this article.

Outside Diameter (OD) vs Inside Diameter (ID)

The inside diameter(ID) and the outside diameter (OD) bear significant differences due to the thickness of the walls. If the thickness moves, the inside diameter changes, and you need to keep that in mind before connecting the pipes—the wall thickness changes in different pipes according to the pipe’s usage.

A thick pipe carries more strength, while a thin pipe is easily bendable. Extra strength work requires Schedule 80, and Schedule 40 is used for common jobs due to its lesser thickness and low price.

Why Nominal Diameter?

As mentioned, you need to convert an actual diameter to a nominal to find the pipe’s right fit. That is not possible with standard diameter.

As the NPS is the standard size of the pipes in North America, it is essential to carry out certain calculations to determine your line’s right size.

Measuring The Pipe With A String Method

Measuring The Pipe With A String Method

A string method is one of the easiest ways to figure out a copper pipe’s length. You will most of the time find a label printed on a pipe indicating its size and type. If the pipe doesn’t have the information printed on it, you can use this method.

This method is useless if you do not have the conversation chart’s final figures. Below is a neatly instructed step by step guide for following the string method

Step 1: Gathering the materials

You will need a string, ruler, marker, and your piece of pipe.

Step 2: Measuring the pipe (Male thread)

Take your pipe and start measuring the outside diameter (OD) and wrap the string around the pipe once. Make sure you are not overlapping the row. One wrap is all that you will ever need. Get a marker and start drawing where the second loop touches the first end of the string.

Step 3: Find the circumference

Keep your ruler on a flat surface and place the string on the ruler to map the thread’s exact length to the marked dot. The number on the scale is the circumference of the pipe.

Step 4: Dividing the number

Divide the ruler number by 3.14159. You need to cross-check the number with the below-given conversion chart.

Measuring the female thread

Step 1: Gathering the materials

You will need a string, ruler, marker, and your piece of pipe.

Step 2: Measure the pipe (Female thread)

Measure the inside diameter (ID) of the pipe and follow the same steps given above.

Step 3: Conversation

Look at the conversation chart to find the nominal diameter (all measurements are in inches):

Inside or outside diameter  Decimal equivalent Nominal diameter Typical threads per inch
5/16 0.313 1/16 27
13/32 0.405 1/18 27
35/64 0.540 1/4 18
43/64 0.675 3/8 18
27/32 0.840 1/2 14
1-3/64 1.050 3/4 14
1-5/16 1.315 1 11-1/2
1-21/32 1.660 1-1/4 11-1/2
1-29/32 1.900 1-1/2 11-1/2
2-3/8 2.375 2 11-1/2
2-7/8 2.875 2-1/2 8
3-1/2 3.500 3 8
4 4.000 3-1/2 8
4-1/2 4.500 4 8


Tips To Keep In Mind

Tips To Keep In Mind

  • If you have tubing instead of piping, there is no need to convert the nominal diameter. Tubing is always named based on the OD, i.e., outside diameter.
  • You can use tables to find the schedule of your copper pipe (see also ‘What Is The Difference Between L And M Copper Pipe?‘). A ‘schedule’ is related to the wall thickness.
  • If you have a cross-linked polyethylene tubing, PEX, then the internal diameter is equivalent to the nominal diameter.

Scientific Tools To Measure Pipes

Apart from the string method, you can use professional tools such as the vernier caliper.  This instrument can be used for several types of measurements. This instrument can measure the diameter, thickness, and even the pipes’ inner diameter.

It generally comes with a scaled handle, two jaws for thickness measurements, and two smaller jaws for measuring the inner diameter of your copper pipe. A vernier caliper gives the reading error of 0.05mm.

Now that you have learned about copper pipe measurement and how to do it, it is imperative to know the types of pipes available in the market.

Good knowledge of pipes can save you money as you won’t keep buying new pipes. There are four types of copper pipings that are available in the market that you should know.

Common Types of Copper Piping

Common Types of Copper Piping

Type K Copper Pipe

Type K copper pipe is the most durable and robust pipe out of all four types because of its thick walls. An ½ inch type K pipe will have a thickness of .049 inches. Similarly, a ¾ inch pipe will have a thickness of 0.65 inches. The pipe’s wall thickness varies according to the pipe’s diameter.

As this pipe is thicker, more metal is used, and thus the cost of this type of pipe is relatively higher. These pipes are not easy to work with, along with being expensive for your standard sink connections. Central underground water installations use these types of lines.

The weight of being buried down will not crush the pipes, and the water will keep flowing without any disturbance. Type K copper pipes are available in both flexible rolls and rigid forms.

These pipes are marked green for easier identification. Copper pipes of type Ks are generally used for underground water installations, commercial use, sprinkler systems, and more.

Type L Copper Pipe

Type L is not as thick as type K pipes, but it is durable and commonly used for many outdoor projects.

If your area or house has a hard water supply, using type L pipe is always recommended. The thick walls will not wear down quickly, even if the water has minerals in it. These types of lines come with a blue mark.

A perfect example for using Type L pipe is hot water heating systems (see also ‘ Pros And Cons Of Hot Water Heating Systems ‘), interior water supply systems, fire protection, and some HVAC applications.

Type L can come in flexible rolls or rigid forms. One can use Type L pipes for compression, sweat, and flare fittings. The price of this pipe is comparatively lower than type K copper pipe.

Type M Copper Pipe

Type M is the thinnest pipe size than type L, and K.The wall thickness of a copper pipe will be .032 inches if the diameter is ¾ inches. This type of pipe is exceptionally lightweight, cheap, and less rigid, meaning you can use Type M pipes for various construction purposes.

Even Type M comes in a flexible roll and rigid tubing, and the differentiator color is Red. Type M copper pipes come in handy for domestic appliances and domestic water systems. These pipes have ample strength that a domestic pipeline works.

Copper DWV Pipe

The letters DWV stands for drain, waste, and vent. Drain and vent lines use this type of pipe. Regular water systems do not use this type of pipe. These pipes’ diameter is more extensive than all styles and comes with a yellow marking. It even has thinner walls than other tubes. 

These pipes can only take a maximum pressure rating of 15 psi. You can easily find these pipelines in old houses. PVC pipes in newer homes have replaced the copper DWV pipe.

There you have it, readers, a quick guide that talks about copper pipes’ basics and how to measure them. Now, whenever you want to do a plumbing job, you do not need to go back and forth to your local hardware store searching and fitting for the right pipe sizes.

author avatar
Charlie Hardcastle


On Key

Related Posts

Is Drano Bad for Pipes? The Truth Revealed

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases. When it comes to dealing with clogged drains, many homeowners turn