Type L and Type M copper of the same size have the same outside diameter, so fittings that go over the outside of the tube fit either one. Type L has the thicker wall, and on rigid tube it’s printed in blue. Type M is thinner and printed in red.
Type K, L and M wall thickness
| Size | Outside (all types) | Type K | Type L | Type M |
|---|---|---|---|---|
| 1/2" | 0.625" (15.9 mm) | 0.049" wall, 0.527" inside | 0.040" wall, 0.545" inside | 0.028" wall, 0.569" inside |
| 3/4" | 0.875" (22.2 mm) | 0.065" wall, 0.745" inside | 0.045" wall, 0.785" inside | 0.032" wall, 0.811" inside |
| 1" | 1.125" (28.6 mm) | 0.065" wall, 0.995" inside | 0.050" wall, 1.025" inside | 0.035" wall, 1.055" inside |
Nominal sizes from the Copper Development Association’s tube tables (Tables 14.2a-c). Other sizes and other kinds of pipe are on the pipe OD pages.
Copper tube’s actual outside diameter is always 1/8" larger than its size name, and for any size Type K has a thicker wall than Type L, and Type L thicker than Type M. The extra wall goes on the inside, so Type M has the largest inside.
For the outside of 1/2", 3/4" and 1" pipe of every material, see 1/2", 3/4" and 1" pipe OD.
How to tell Type L from Type M
- The print line: hard (rigid) copper tube is printed with its type in a color: blue for Type L, red for Type M, green for Type K and yellow for DWV drain tube.
- The stamp: every type, rigid or soft, is also stamped (incised) with its type, the maker’s name or trademark and the country of origin. Look along the tube when the print has worn off.
- Soft coils: the CDA’s table of standard lengths lists soft (annealed) coils for Types K and L only, and Type M as hard straight lengths. Makers can sell other lengths, so read the stamp to be sure.
- Measuring: the outside is no help. At a cut end, a caliper across the wall shows the difference: at 3/4", about 0.045" for Type L and about 0.032" for Type M (nominal).
For telling copper from PEX, CPVC or galvanized pipe first, see what pipe do I have?
Do the same fittings fit Type L and Type M?
Fittings that go over the tube are sized by its outside, which every type of one size shares. SharkBite’s Max push-to-connect fittings are one example: its 3/4" fitting is sized 3/4" CTS, for pipe 7/8" across, and is approved for copper made to ASTM B 88, the standard Types K, L and M are all made to. See SharkBite fittings.
A part that goes inside the tube is different, because the inside depends on the wall. Woodford’s combination “C” inlet on its Model 17 wall faucet takes 1/2" Type K, L or M inside it, but slides inside 3/4" tube only if it’s Type M. 3/4" Type L is 0.785" inside, 0.026" narrower than Type M’s 0.811".
Where each type is used
Plumbing and mechanical codes govern which types may be used, and the handbook leaves the pick to the system’s designer. Where a choice can be made, the CDA’s handbook recommends:
- Water distribution (the pipes inside the house): Type M, above and below ground.
- Underground water service (from the main to the house): Type M hard for straight lengths joined with fittings, and Type L soft where coils are more convenient.
- Radiant, hydronic and snow melting heat: Type L soft where coils are formed in place, Type M where straight lengths are used.
- Drains, waste and vents: Type DWV.
Your local plumbing code decides which type your job needs: check with your building department before you choose. Rated working pressures for each type, by temper and temperature, are in the CDA’s Tables 14.3a-d.
Shut off the water and drain the line before you cut into copper pipe. What Adapter For covers water pipe, not gas lines.