Copper Pipe and Tube Dimensions & Specifications

A 1/2" copper pipe measures 0.625" across the outside and nothing about it is half an inch. Copper is sold in copper tube size (CTS), where the outside diameter is always the nominal size plus 1/8". Wall thickness is what changes between Type K, L and M — the outside diameter does not, which is why one fitting size accepts all three types.

This page gives the real dimensions for the copper we stock, plus the four sizing systems that get confused with each other and the rules that decide which type a job is allowed to use.

Copper tube dimensions — Type K, L and M (ASTM B88)

Nominal OD (in) Type K Type L Type M
Wall ID Wall ID Wall ID
1/4" 0.375 0.035 0.305 0.030 0.315 — —
3/8" 0.500 0.049 0.402 0.035 0.430 0.025 0.450
1/2" 0.625 0.049 0.527 0.040 0.545 0.028 0.569
5/8" 0.750 0.049 0.652 0.042 0.666 — —
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

All dimensions in inches. OD is identical across all three types at a given nominal size — that is the whole point of the system, and the reason a 3/4" sweat coupling fits 3/4" K, L and M alike.

Reading the print — the colour code

Every length is line-marked, and the ink colour identifies the type without measuring anything:

Type Marking Wall Where it is used
K Green Heaviest Underground water service, fire protection, and anywhere the tube is buried or takes abuse
L Blue Medium The general-purpose choice: interior water distribution, hydronic heating, commercial work
M Red Thinnest Interior water distribution and hydronic where code permits — the economical option
DWV Yellow Thinner than M Drain, waste and vent only. No pressure service, ever

Type M is the one to check against your code. Many jurisdictions prohibit Type M underground entirely, and some restrict it inside the building as well. The tube is legal to sell everywhere and not legal to install everywhere — confirm with the authority having jurisdiction before you buy for a permitted job.

Hard or soft — temper

The same Type L can arrive as rigid straight lengths or as a coil you can bend by hand. That is temper, and it is a separate decision from type.

  • Drawn / hard (H58) — rigid, sold in straight lengths, higher strength. Standard for exposed and in-wall runs. It cannot be bent; direction changes need fittings.
  • Annealed / soft (O60) — sold in coils, bends with a tool, and can be flared. Standard for underground water service, where a continuous coil under a slab or driveway means no buried joints at all — the joint is what fails underground, so eliminating it is the point.

Soft temper has a lower allowable working pressure than hard temper of the same type and size. Bending also thins the outer wall of the bend, so respect the minimum bend radius and use a bender rather than knees and thumbs.

Copper DWV (ASTM B306)

DWV copper is thinner than Type M and carries no pressure rating. It shares the CTS outside diameter, so it takes DWV-pattern fittings of the same nominal size, but the wall is minimal because gravity drainage asks nothing of it.

Nominal OD (in) Wall (in)
1-1/4" 1.375 0.040
1-1/2" 1.625 0.042
2" 2.125 0.042
3" 3.125 0.045
4" 4.125 0.058

DWV fittings also have drainage-pattern geometry — long sweeps and directional tees that keep solids moving. A pressure fitting and a DWV fitting of the same size are not the same part, and neither substitutes for the other.

ACR tube is sized differently — and this is the trap

Refrigeration tube to ASTM B280 is designated by its actual outside diameter, not by a nominal size. Everything else on this page is nominal, so the two systems collide:

You ask for CTS (B88) gives you ACR (B280) gives you
3/8" OD 0.500" OD 0.375"
1/2" OD 0.625" OD 0.500"
3/4" OD 0.875" OD 0.750"

So a 1/2" ACR tube is the same diameter as a 3/8" CTS tube. Order across the two systems by name and you get the wrong part every time. ACR runs in the odd sizes — 1/4", 3/8", 1/2", 5/8", 3/4", 7/8", 1-1/8", 1-3/8", 1-5/8", 2-1/8" — and those 1/8" fractions are the tell that you are looking at an ACR size.

ACR tube is also cleaned, dehydrated and nitrogen-charged with the ends capped, because moisture and oil in a refrigerant circuit destroy the compressor. Once the caps come off, the clock is running. Wall thickness varies with size and temper, so take it from the print rather than from a general table.

Working pressure — the joint governs, not the tube

Copper tube itself is far stronger than any plumbing system needs. In a soldered system the limit is almost never the tube — it is the filler metal, and it falls off sharply as temperature rises. Ranked from weakest to strongest:

  1. 50-50 tin-lead solder — the lowest rating, and illegal on potable water in the United States since 1986. It still exists for non-potable work.
  2. Lead-free solder (ASTM B32) — tin-antimony, tin-silver and similar. Considerably stronger than 50-50 and required on anything carrying drinking water.
  3. Brazed joints — filler above 1,000°F, typically AWS BCuP alloys. Several times the strength of any soldered joint, and what refrigerant and medical gas work uses.
  4. Press and mechanical joints — rated by the fitting manufacturer to their own listing rather than by a filler metal.

Because the rating depends on type, size, temper, filler metal and service temperature all at once, there is no single number for "copper pipe pressure rating". Take the figure from the Copper Development Association rated-internal-working-pressure tables for the exact combination you are installing, and confirm the filler metal is listed for the service.

Lead-free is a legal requirement, not a preference. Solder and flux for potable water must contain no more than 0.2% lead, and wetted components must meet a 0.25% weighted-average lead limit under NSF/ANSI 372. Keep leaded solder off the truck if you do potable work — the failure mode is a failed inspection at best.

Joining methods

Method Fitting standard Notes
Solder (sweat) ASME B16.22 wrought, B16.18 cast Lowest cost per joint. Needs a dry line, a flame and a hot work permit in many buildings
Braze Same fittings, AWS BCuP filler Required for refrigerant and medical gas. Nitrogen purge while brazing
Press ASME B16.51 No flame, no dry line. Proprietary jaw profiles — match fitting to tool
Push-to-connect Manufacturer listing Fastest, highest cost per joint. Check whether your code allows them concealed
Compression Manufacturer listing Serviceable, for accessible locations
Flare ASME B16.26 Soft temper only — hard drawn tube cracks when flared
Grooved Manufacturer listing Large diameter, fast assembly, allows movement at the joint

Whatever the method, the preparation is the same and it is where joints are won or lost: cut square, ream the burr, clean the tube end and the socket to bright metal, and keep the seal area free of scoring. A burr left inside the tube causes erosion-corrosion downstream for the life of the system — a slow failure that gets blamed on water chemistry years later.

Standards referenced

  • ASTM B88 — Seamless copper water tube, Types K, L and M.
  • ASTM B306 — Copper drainage tube (DWV).
  • ASTM B280 — Seamless copper tube for air conditioning and refrigeration field service (ACR).
  • ASTM B819 — Seamless copper tube for medical gas systems.
  • ASTM B32 — Solder metal, including the lead-free alloys.
  • ASME B16.22 / B16.18 — Wrought and cast copper solder-joint pressure fittings.
  • ASME B16.29 / B16.23 — Wrought and cast copper solder-joint DWV fittings.
  • ASME B16.26 — Cast copper alloy fittings for flared tube.
  • ASME B16.51 — Copper and copper alloy press-connect pressure fittings.
  • NSF/ANSI 61 and 372 — Drinking water system components, and the lead-content limit.

Shop copper

Need a submittal or a sizing check on something we stock? Call +1 (623) 307-5144 or email info@thehousesupplier.com.