ASTM B88 · Copper tube explained

How copper tube sizes work

Nominal size vs actual OD, what Type K, L, M, and DWV mean, the color codes, and how to work out ID and weight yourself — with worked 1/2" and 3/4" Type L examples.

Where to get the dimensions

Type K, L, and M water tube is standardized in ASTM B88 (DWV tube: B306; ACR tube: B280), published by ASTM International. The Copper Development Association (copper.org) publishes the free Copper Tube Handbook with dimensions, weights, pressure ratings, and joining practice, and every tube manufacturer publishes its own data.

Which types are allowed for which service is set by your adopted plumbing or mechanical code (IPC, UPC, IMC, or local amendments) and the project spec — verify against the edition adopted by your AHJ.

Tube types, color codes, and where they are used

Type	Marking color	Typical use
Type K	Green	Thickest wall. Underground water services, fire protection, high-pressure and critical service. Available hard or soft (coils).
Type L	Blue	Medium wall. The workhorse for interior water distribution, hydronic heating, and many commercial specs. Available hard or soft.
Type M	Red	Thinnest pressure-rated wall. Residential and light-commercial water where the code allows. Usually hard (straight lengths) only.
DWV	Yellow	Drain, waste, and vent — non-pressure. Not for water supply.
ACR	Varies by maker	Air conditioning and refrigeration. Named by actual OD, cleaned and capped for refrigerant service. Do not substitute plumbing tube for refrigerant lines.
Medical gas	Varies by maker	Type K or L tube cleaned and capped for oxygen/medical gas service. Installed under NFPA 99 by certified installers.

Typical practice — allowed uses are set by your adopted code and project specification.

Worked examples

Example	Input	Steps	Result
A. 1/2" Type L	Nominal 1/2". OD = 1/2 + 1/8 = 0.625 in. Wall 0.040 in (manufacturer data).	ID = 0.625 − 2(0.040) = 0.545 in. Metal area = π × (0.625 − 0.040) × 0.040 = 0.0735 in². Weight = 0.0735 × 12 in × 0.323 lb/in³ = 0.285 lb/ft.	ID 0.545 in · ≈ 0.285 lb/ft
B. 3/4" Type L	Nominal 3/4". OD = 3/4 + 1/8 = 0.875 in. Wall 0.045 in.	ID = 0.875 − 2(0.045) = 0.785 in. Water-carrying area = π × 0.785² ÷ 4 = 0.484 in².	ID 0.785 in
C. Why the upsize matters	Compare flow area: 1/2" L vs 3/4" L.	1/2" L area = π × 0.545² ÷ 4 = 0.233 in². 0.484 ÷ 0.233 ≈ 2.1.	3/4" L has about twice the flow area

Wall thicknesses quoted only to illustrate the math. Get other sizes and types from the CDA Copper Tube Handbook or the manufacturer.

Common field mistakes

Mistake	What to do instead
Calling tube by its measured OD	Tube that measures 5/8" is 1/2" nominal plumbing tube (or 5/8" ACR). Know which system you are in before ordering fittings.
Using plumbing tube for refrigerant	ACR tube is cleaned, capped, and sized by OD. Plumbing tube can contaminate a refrigerant system and the sizes are named differently.
Type M where it isn't allowed	Some jurisdictions and most commercial specs exclude Type M. Check the code and spec before bidding it.
Annealing hard tube with heat and forgetting it	Brazing softens (anneals) drawn tube, lowering its rated pressure. Rated pressures for brazed joints are lower than for the tube itself.
No pressure test record	Log the test pressure, duration, gauge, and witness for each section before cover-up.

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Type K, L, and M copper

Plumbing copper tube uses a nominal size, and the actual outside diameter is the nominal size plus 1/8". At a given size, Types K, L, and M all share that OD so they take the same fittings — the difference is the wall: K thickest, L medium, M thinnest.

The wall sets the inside diameter, weight, and pressure rating. With the wall from the manufacturer or CDA data, ID = OD − 2 × wall, and weight follows from copper's density (about 0.323 lb/in³). Printed line colors — K green, L blue, M red, DWV yellow — let you ID hard tube on site.

For steel and process piping, see how steel pipe schedules work and how NPT threads work. Field PM keeps mechanical submittals, pressure-test records, and QA/QC in one place from rough-in to closeout.

FAQ

What is the difference between Type K, L, and M copper?+

Wall thickness. At a given nominal size all three share the same outside diameter, so they use the same fittings. Type K has the thickest wall, Type L is medium, and Type M is the thinnest. Thicker wall means a smaller inside diameter, more weight, and a higher pressure rating.

Is copper tube sized by OD or ID?+

Neither, for plumbing tube. Type K, L, M, and DWV use a nominal size, and the actual outside diameter is the nominal size plus 1/8 inch — 1/2" nominal tube is 5/8" (0.625") OD. ACR tube for refrigeration is the exception: it is named by its actual OD.

Which copper type for water lines?+

Type L is the common choice for interior water distribution and is often required by commercial specifications. Type M is permitted for many residential and some commercial water systems, and Type K is typical underground and for higher-pressure or critical service. The adopted plumbing code and the project spec decide.

What do the colors on copper tube mean?+

The printed marking color identifies the type on hard (drawn) tube: Type K green, Type L blue, Type M red, and DWV yellow. Annealed (soft) coils are generally not color-marked the same way, so check the stamped marking.

What is the ID of 1/2" Type L copper?+

About 0.545". It has a 0.625" OD and a 0.040" wall, so ID = 0.625 − 2 × 0.040 = 0.545". Its weight works out to about 0.285 lb/ft.

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