What do the letters ‘K,’ ‘L’ and ‘M’ on copper tubing mean?

What Do K, L, and M Mean on Copper Tubing?

K, L, and M are markings on copper tubing that identify the pipe’s wall thickness and type.

• K = Type K copper (thickest wall)

• L = Type L copper (medium wall)

• M = Type M copper (thinnest wall)

These markings help determine the pipe’s strength, pressure rating, and proper use.

What’s the Difference Between Type K, L, and M Copper?

The main difference is wall thickness and pressure capacity.

• Type K 
  Thickest wall. Highest durability and pressure rating.
  Common for underground water service lines.

• Type L 
  Medium wall thickness. Strong and versatile.
  Most commonly used for interior residential water supply lines.

• Type M 
  Thinnest wall. Lower pressure rating.
  Often used for residential plumbing where local code allows.

Where to Find the Right Copper Tubing

At Westlake Ace Hardware, you’ll find Type K, L, and M copper tubing, fittings, soldering supplies, and plumbing tools. Our associates can help you match the correct pipe type to your plumbing application and local building requirements.

When Should You Use Type K, L, or M Copper?

When to Use Type K

Use Type K copper when maximum strength and durability are required.

Common applications:

• Underground water service lines (from the meter to the home)

• High-pressure water systems

• Direct burial installations

• Commercial plumbing systems

Type K has the thickest wall and highest pressure rating, making it ideal for demanding environments.

When to Use Type L

Use Type L copper for most residential and interior plumbing projects.

Common applications:

• Interior hot and cold water supply lines

• Main water distribution lines inside the home

• Fire sprinkler systems (where permitted)

• General-purpose residential plumbing

Type L offers a balance of strength, durability, and cost, making it the most commonly used copper pipe in homes.

When to Use Type M

Use Type M copper for lighter-duty residential applications where allowed by local code.

Common applications:

• Branch water supply lines

• Repair or retrofit plumbing work

• Low-pressure residential systems

Type M has the thinnest wall and lowest pressure rating of the three types, so it is typically used only in standard residential water distribution systems.

Important Note

Always check local plumbing codes before choosing a copper pipe type. Some municipalities restrict the use of Type M for certain water supply applications.

Check your state and local codes before starting any project. Follow all safety precautions. Every effort has been made to ensure the accuracy and safety of this information. Neither Westlake nor any contributor can be held responsible for damages or injuries resulting from the use of the information in this document.