Copper pipe types K, L and M

Entry in Metal pipe · Updated October 29, 2026 · Written by the Know Your Pipes editors from the sources listed under References

Copper pipe types K, L and M are the three wall-thickness grades of copper water tube made to ASTM B88: type K has the heaviest wall, type L a medium wall and type M the lightest wall^[1]. In the type L vs type M copper comparison, the practical difference is wall thickness, which changes weight, pressure rating and where codes allow each one.

All three are made from the same copper alloy, UNS C12200, and the type letter describes the wall rather than a different metal or a quality grade^[1]. A separate yellow-marked grade, made to ASTM B306, is used for drainage and is covered under copper DWV pipe^[1].

1 Identification

Hard (drawn) tube carries a continuous printed line in a color that names the type: green for K, blue for L and red for M^[1]. Makers also incise (stamp) each length, so the type can still be read after the ink wears away^[3]. Soft annealed tube in coils or straight lengths is not color-marked, so the incised mark is the way to read it^[1].

Two lengths of the same nominal size can look identical from outside. Reading the print line or the stamp is the reliable test; reading pipe markings explains the other text found on the line.

Source for the table: one maker's published product range^[1]. Other mills may offer different coil lengths.

2 Pressure ratings

For a given nominal size, the heavier wall carries the higher allowable pressure^[2]. Makers publish rated working pressures calculated for annealed tube, which is the condition to use when joints are soldered or brazed, because heat softens hard tube near the joint^[2]. Higher ratings for hard tube apply only to systems joined without heat, such as flare or compression joints^[2].

The figures above come from one maker's submittal and are computed values for the tube alone^[2]. A finished system is rated by its weakest part, so fittings, valves and joints set the real limit. Weight follows the same order: 1/2 in tube weighs about 0.344 lb/ft as type K, 0.285 lb/ft as type L and 0.204 lb/ft as type M^[2].

3 Typical uses

One maker describes type M for above-ground residential and light commercial work, type L for residential and commercial work, and type K for underground service in homes, commercial buildings and industry^[1]. The same maker lists types K and L for water service and distribution, fire protection, HVAC, fuel oil, compressed air, natural gas and liquefied petroleum gas, and type M for general plumbing, heating and other light-pressure uses^[1].

Which type a given job may use is decided by the plumbing or fuel gas code in force, not by the tube maker, and makers say so in their literature^[1]. The model codes are discussed under plumbing codes; local amendments are common, and the building department decides questions of approval. Copper used for gas is a separate case with its own code rules and is work for a licensed installer.

4 Material and drinking water

Copper water tube under ASTM B88 has a minimum copper content of 99.9% with phosphorus between 0.015% and 0.040%^[4]. Makers certify the tube to NSF/ANSI/CAN 61 for drinking water with a pH of 6.5 or higher; supplies below pH 6.5 may need corrosion control to limit copper leaching^[2].

Under federal law, pipe and fittings sold as "lead free" for drinking water must average no more than 0.25% lead across wetted surfaces, and solder and flux no more than 0.2%^[5]. Copper tube meets this easily; the lead question in older copper systems is usually the solder, as described under lead-free solder. Water chemistry, velocity and workmanship affect how long copper lasts; pinhole leaks in copper covers the common failure.

5 Joining

Hard and soft copper tube is joined by soldered (sweat) joints, brazing, press fittings, flare or compression fittings and push-fit fittings. Each method has its own fittings standard, tool and maker's instructions; see soldered sweat joints, copper press fittings and push-fit fittings. Of these, push-fit is the only one suited to a homeowner's emergency repair, and then only if both the fitting maker and the local code permit it.

Where copper meets galvanized steel, a dielectric union or brass fitting is used to slow galvanic corrosion. Supply houses stock tube by type, temper and length; PlumbingSupplyAndMore's copper pipe category (PlumbingSupplyAndMore has the same owners as this reference) is one example of how the types are listed.