Copper Pipe & Tube Size Chart

In the United States, the state or region you reside dictates the residential and commercial building codes. Advancements in technology and building materials triggered changes in the building codes. The recent changes include permitting copper tube sizing (CTS) piping in residential plumbing solutions.


Copper pipes & tubes are the most popular throughout the United States, which is why you need a size chart to be sure you get the right one. We’ve included one below to help you out.

In this article, we also look at the following:

  • Its uses
  • The types
  • Connectors

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This red metal has served many advancements in civilization. Several tools for agriculture and handicraft, articles for household items and decoratives, and hunting weapons utilize this metal.

We recognize it in modern technology because there is no other superior material for transporting water. Several years of proven durability that serves its purpose backs it up.

We use it nowadays in several home applications, such as heating, air-conditioning, and plumbing. Copper pipe is available in different sizes, types, and thicknesses. Fittings are available for almost all design applications.

The allowance of these copper water lines will surely interest some people. We are walking you through everything you need to know about CTS tubing. 

Copper pipe & tube size chart

The table below is a detailed explanation of its sizes. You can determine the nominal size using the outer diameter (OD). On the other hand, wall thicknesses and inner diameter (ID) vary per type.

For example, a Type K has an internal diameter of 0.305 and a wall thickness of 0.035. A type L has an internal diameter of 0.315 and a wall thickness of 0.030. However, both share the same outer diameter of 0.375 and a nominal size of 1/4.

Nominal Pipe Size inchesO.D.K*, I.D.K, Wall ThicknessL**, I.D.L, Wall ThicknessM***, I.D.M, Wall ThicknessDWV****, I.D.DWV, Wall Thickness
Copper Pipe

The wall thickness determines the inside diameter, while the nominal size determines the outside diameter of a rigid copper. The OD is always 1/8 inch larger than the nominal size.

What is a CTS pipe?

We use copper tube sizing (CTS) in heating, water supply, and HVAC applications. These are available in two types – rigid and soft. Mechanics use a flare connection, solder, compression connection, or pressed connection to join two tubes.

Copper tubing

Rigid Type

Water lines are the main application for rigid copper. Mechanics join pipes together using compression, roll grooved, or solder.

These are rigid because of the hardening it goes through during the drawing process. You cannot bend it, so you need to use elbow fittings to go around obstacles. Alternatively, annealing softens it. It allows you to bend or form the material without cracking.

Soft Type

Ductile or soft copper tubing easily bends to go over obstacles in its path. The hardening process makes it rigid, but careful annealing makes it soft again.

As a result, it becomes more expensive than the rigid type. You can join two tubes by roll grooved, solder, or compression. It is the preferred option for heat pumps and split-type air conditioner systems.

What are the connection types?

There are a few ways to connect two tubes. The following are the most common methods of doing it.

Brazing Connection

Brazing is a joining process involving two or more metal items. We join these by melting and pouring a filler metal into the joint. The filler metal should have a lower boiling point so they will not melt together.

Welding is different from brazing because the former involves melting the work pieces. On the other hand, soldering does not require closely fitted parts.

Capillary action allows the filler to flow through the gaps. The filler metal slightly goes over its melting temperature while getting protection from a flux.

It goes through a wetting process before allowing it to cool down. An advantage of brazing is allowing you to join different or the same metals. The filling material should have a melting point above 427 Celcius.

Soldered Connection

Solder fittings slip into the end of the other tube without issues. A mechanic heats the joint using a torch to melt the connection. It forms a strong bond after the cooldown, lasting several decades. 

Most modern buildings use a solder connection for their supply lines. Soldering is more cost-effective than flaring, which is more evident in large-scale applications.

We also use the term sweating when referring to soldering. You can interchangeably use these two terms. The filling material should have a melting point below 427 C.

Flare Connection

A flare connection will require an outward spreading of one end of the tubing to a bell shape using a flare tool. We use a flare nut to fit the end onto a male fitting. The flare connection is the most work-intensive type but pays off because of its reliability. 

Compression Connection

Compression fittings utilize a thermoplastic ring or a soft metal. It squeezes onto the pipe and into the fitting using a compression nut. The thermoplastic ring or soft metal shapes onto the tube’s surface and creates a sealing effect.

The disadvantage of a compression fitting is its longevity, which has a shorter lifespan than a sweat connection. Its advantage is the easy installation using standard tools. Maintenance is also more frequent with this connection.

Pressed or Crippled Connection

The last type is the crippled connection, which utilizes special copper fittings permanently attached to copper tubing. These already have a sealant inside.

Deforming the fittings takes thousands of pounds-force per sq. inch of pressure. Compressing it pushes the bond against the inner tubing, creating a tight seal.

The following are the advantages of the crippled connection.

  • It is long-lasting
  • It takes less time than other methods
  • The final appearance looks clean
  • It does not need open-flame during the installation process

However, the disadvantage is the availability of the parts. It impacts the cost in the long run.

What are copper pipes used for?

thicker copper pipe

We use copper pipes in the water line and heating systems. For several years, we heavily depend on copper to satisfy these applications. However, recent technological advancements have introduced PEX.

One of their primary purposes is to deliver safe, clean water. It can either be hot or cold, potable or non-potable. Aside from providing a drinking water supply, we also use it to:

Water Service and Distribution

We use it to transport safe, clean water through several domestic applications. Copper has proven to deliver a cost-effective and reliable water supply. 

Refrigeration and Air Conditioning

We have air conditioning at home to make our living conditions more comfortable, productive, and safe.

Copper helps us cool in the summer and warm in the winter by offering resistance to extreme weather conditions. It offers corrosion resistance, making it last longer and requires less maintenance.

Vacuum and Medical Gas

Hospitals and other medical facilities use copper linings to deliver medical gases needed in treatment and recovery.

We need gasses, such as carbon dioxide, nitrous oxide, and nitrogen, in healthcare facilities. This metal prevents microbial buildup in gas systems, so they remain pure and contaminant-free. 

Fire Sprinklers System

Sprinkler systems serve as another security layer in case of fire. The reliability of copper makes it an excellent material in fire sprinkler systems. It will not support combustion, decompose to toxins, or carry fire. In emergency situations, it will continue delivering water to the sprinklers. 

Fuel Distribution

Smaller tubes and fittings are effective against delivering gases in non-residential and residential buildings. All major codes in the United States recognize it for fuel gas distribution systems. 

Other Relevant Applications

Other applications, such as snow melting, agricultural sprinkler, drain vent, and geothermal cooling/heating, are where you can take advantage of copper. 

The most common types you will find in the market are types L, M, and K. You will find more details and explanations in the following sections. 

Type L

Type L Copper Pipe

We use Type L in fire protection, HVAC, and plumbing applications. These are available in soft or rigid forms. It makes them compatible with flare, compression, and sweat fittings. We consider the L-type the most common one in the market. You can use it in more applications than the K-type.

You can use the flexible one for old water line replacement or repair. However, the rigid form is more durable. You can use it outdoors under direct sunlight exposure. These are particularly best for interior water lines. Type L is thinner than K but thicker than M. 

Type M

Type M is thinner than L or K. It is also available in soft and rigid forms. Its typical applications are vacuum and domestic water service systems.

We can use flare, compression, or sweat fittings to join two tubes. It is also a favorite choice for residential applications because it is cheaper. Thinner walls mean there is less copper in the material. It translates to a lower manufacturing cost, affecting the retail price of these items.

The caveat here is that several plumbing codes in the United States do not permit the use of M copper. We recommend checking with the local authorities for restrictions. 

Copper Type M Pipe

Type K

Type K has the thickest wall among the three. We recommend using it for:

  • HVAC
  • water distribution
  • oil
  • fire protection
  • and other construction industry applications.

It is available in soft or rigid forms, allowing you to use compression or flare fittings.

Underground installations and water lines are some of the major application strengths of Type K. Its thickness help withstand pressure underground. Avoid using it for handling natural gas applications because it can damage the joints.

Type K Copper 1”

Copper type L vs. M

These two may have the most similar applications among the three. The difference lies in the wall thickness and pressure rating, with 1/2 and 3/4 inches being the standard sizes most applications need.

In terms of cost, Type L is more expensive than the M because it has thicker walls. It also needs more copper material to manufacture, adding cost to the production process. Transportation cost is also higher because it weighs more. 

In comparison, a 3/4 inch type L has a working pressure of 1,002 lbs / square inch, while type M rates at 701 lbs / square inch. The pressure decreases as the pipe diameter increases. Let us use the L type to compare. A 1/2-inch has a maximum working pressure of 1,242 lbs / square inch. In contrast, a 1-inch rates 850 lbs / square inch. 

Copper pipe types

copper pipe fittings male adapter

We discussed in the previous sections the three types – L, K, and M. However, there is a fourth type called copper DWV pipe. It stands for drain, waste, and vent. By its name, its only approved use is in vent and drain lines.

It is the only copper type not primarily used in water systems, making it the odd one among them. These come in larger diameters than the rest. It also has thinner walls, allowing it to withstand a maximum pressure rating of 15 psi.

You will only find this in older homes. Newer homes use PVC pipes because DWV is already obsolete. 

Tube vs. pipe

Copper Water Pipe 2 1 2 x 35

Most people interchangeably use these two terms. They are similar in several aspects, but there is one particular distinction between them.

We usually use tubes in structural applications, so the outside diameter is more relevant. We also use it in medical applications, especially devices requiring precise outside diameters.

We use pipes to transport liquids to gases, making capacity important. Knowing how much can flow through it is the answer. We classify pipes through nominal diameter and schedule size. Manufacturers sell these in nominal pipe size (NPS) standard and wall thickness. 

Different pipe sizes can have the same NPS but have different wall thicknesses. On the other hand, manufacturers sell tubes by wall thickness and outside diameter. The gauge number defines the thickness of the walls, with a larger gauge number indicating a smaller diameter.

The following are some characteristics of pipes and tubes.


Pipes are round. Tubes can come in rectangular, round, or square shapes.

Telescoping Attributes

You can telescope a tube. It is a perfect application to sleeve different pieces or expand inside one another.


You can bend or coil tubes without getting too much wrinkling, distortion, or fracturing. On the other hand, pipes are generally rigid and need special equipment to morph.

How to measure copper pipe

Here is a step-by-step guide to measuring your copper pipe size. You only need four materials – the pipe, a string, a ruler, and a marker.

  1. Wrap the string around the pipe once. Mark the section where it overlaps.
  2. Place the string on a flat surface. Measure the length using a ruler or a tape measure.
  3. Divide the resulting length by 3.143. This value represents the outer diameter.
  4. Subtract 1/8 inches or 0.125 inches from the outer diameter to get the nominal pipe size (NPS).

What is 1/4 copper tubing?

A 1/4 copper tubing with an outside diameter of 0.375 inches. The inner diameter and wall thickness vary.

TypeInner DiameterWall Thickness

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