What is copper pipe Type L vs Type M?
Type L and Type M are copper pipe grades defined by wall thickness, with Type L having thicker walls for higher pressure tolerance and Type M suitable for standard residential water supply.
Copper comes in several wall-thickness grades, with Type L and Type M being the most common in residential plumbing. The letters indicate the thickness of the copper walls: Type M has thinner walls, while Type L has significantly thicker walls. This difference directly affects how much pressure each type can safely handle.
Type M copper is the standard choice for interior residential water lines in most homes. Its thinner walls keep material costs lower while still meeting code requirements for typical household water pressure (usually 40 to 80 pounds per square inch). You will see Type M used for both hot and cold water supply lines running through walls and under floors.
Type L copper has thicker walls and higher pressure ratings, making it better suited for areas where the pipe might face more stress or where local code requires it. Some plumbers in Aiken, SC use Type L for main water service lines entering the home or in commercial applications, though residential work typically stays with Type M.
Both types are measured by outside diameter (such as 1/2 inch or 3/4 inch), but their internal diameters differ because of the wall thickness. A plumber choosing between them must consider local code, water pressure conditions, and whether repiping work requires upgrading the entire system. Type M is cheaper and faster to install, while Type L lasts longer under high-stress conditions.