ASTM B88 · Copper tube
Outside diameter, wall thickness, and inside diameter for Type K, L, and M copper tube from 1/2" to 4" — the dimensions for plumbing, hydronic, and refrigerant lines.
| Nominal | OD (in) | K wall | K ID | L wall | L ID | M wall | M ID |
|---|---|---|---|---|---|---|---|
| 1/2" | 0.625 | 0.049 | 0.527 | 0.040 | 0.545 | 0.028 | 0.569 |
| 3/4" | 0.875 | 0.065 | 0.745 | 0.045 | 0.785 | 0.032 | 0.811 |
| 1" | 1.125 | 0.065 | 0.995 | 0.050 | 1.025 | 0.035 | 1.055 |
| 1-1/4" | 1.375 | 0.065 | 1.245 | 0.055 | 1.265 | 0.042 | 1.291 |
| 1-1/2" | 1.625 | 0.072 | 1.481 | 0.060 | 1.505 | 0.049 | 1.527 |
| 2" | 2.125 | 0.083 | 1.959 | 0.070 | 1.985 | 0.058 | 2.009 |
| 2-1/2" | 2.625 | 0.095 | 2.435 | 0.080 | 2.465 | 0.065 | 2.495 |
| 3" | 3.125 | 0.109 | 2.907 | 0.090 | 2.945 | 0.072 | 2.981 |
| 4" | 4.125 | 0.134 | 3.857 | 0.110 | 3.905 | 0.095 | 3.935 |
Drawn copper tube per ASTM B88. Outside diameter is the same for all three types at a given size (OD = nominal + 1/8"); the wall thickness — and therefore inside diameter and pressure rating — sets the type. Type K is thickest, then L, then M.
Copper tube comes in three common wall thicknesses. At a given nominal size all three have the same outside diameter (nominal + 1/8"), so they use the same fittings — the difference is the wall: Type K thickest, Type L medium, Type M thinnest.
That wall sets the inside diameter and the pressure rating. Type K serves underground and high-pressure runs, Type L is the workhorse for interior water distribution (and commonly spec'd in commercial), and Type M is used for residential water where the code allows. Printed line colors — K green, L blue, M red, DWV yellow — let you ID the type on site.
For larger steel and process piping, see the pipe schedule chart. Field PM keeps your mechanical submittals, pressure-test records, and QA/QC in one place from rough-in to closeout.
All three share the same outside diameter at a given size; they differ in wall thickness. Type K is the thickest (underground and high-pressure service), Type L is medium (interior water distribution, common in commercial), and Type M is the thinnest (residential water lines where allowed by code).
Copper tube uses a nominal size that is neither the OD nor the ID — the actual OD is the nominal size plus 1/8". A "1/2-inch" Type L tube has a 0.625" OD and roughly a 0.545" ID.
Type L is the common choice for interior potable water distribution and is required by many commercial specs; Type M is permitted for residential water in many jurisdictions; Type K is used underground and for high-pressure or critical service. Always confirm with the local plumbing code.
Printed line color: Type K = green, Type L = blue, Type M = red, and DWV = yellow. The marking lets you identify the type on site without measuring the wall.
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