Air Conditioning and Refrigeration (ACR) copper tubing is generally identified by its outside diameter rather than the nominal sizing convention commonly used for plumbing copper tubing.

The following chart lists common ACR copper tubing sizes and their outside diameter conversions from inches to millimeters.

Find common ACR tubing outside diameters and their metric equivalents.

Note: Values show are nominal outside diameter conversions from inches to millimeters, rounded to three decimal places. Actual dimensions are subject to manufacturing tolerances. Verify product specifications before selecting tubing or fittings.

ACR stands for Air Conditioning and Refrigeration. ACR copper tubing is designed for use in refrigerant piping systems, including residential air conditioning, commercial refrigeration, heat pumps, and other HVAC applications.

Copper tubing used for refrigeration must meet requirements related to cleanliness, dimensional consistency, and compatibility with the intended operating conditions.

In North America, ASTM B280 is a commonly referenced standard for seamless copper tubing intended for field air conditioning and refrigeration applications.

Unlike general-purpose plumbing tubing, ACR tubing is typically prepared to minimize contamination inside the tube. Depending on its form, it may be dehydrated, cleaned, and sealed at the ends to protect its internal surfaces before installation.

These characteristics help reduce the introduction of moisture, particles, and other contaminants into refrigerant systems.

For more information about ACR copper tubing requirements, refer to ASTM B280: Standard Specification for Seamless Copper Tube for Air Conditioning and Refrigeration Field Service.

One of the most important distinctions when selecting refrigeration copper tubing is the difference between outside diameter and inside diameter.

The outside diameter is the distance across the exterior of a copper tube. This measurement is commonly used to identify ACR tubing sizes and determine compatibility with refrigeration fittings.

For example, a 7/8″ ACR copper tube has a nominal outside diameter of 7/8″, equivalent to 22.225 mm.

The inside diameter represents the internal opening through which refrigerant flows.

Unlike the outside diameter, the inside diameter changes depending on the tube’s wall thickness.

A thicker wall reduces the available internal diameter even when the outside diameter remains the same.

The approximate inside diameter of a copper tube can be calculated using the following formula:

Inside Diameter = Outside Diameter − (2 × Wall Thickness)

For example, consider a copper tube with:

0.875 − (2 × 0.045) = 0.785″

The resulting nominal inside diameter is approximately 0.785″, or 19.939 mm.

This calculation illustrates why tubing with identical outside diameters can have different internal dimensions depending on wall thickness.

Note: This is an illustrative dimensional calculation. Always confirm actual tube specifications and manufacturing tolerances.

Copper tubing wall thickness plays an important role in determining its mechanical strength, internal flow area, and suitability for the intended application.

While outside diameter identifies the tube’s general size, wall thickness is a separate specification that must be verified when selecting tubing for a refrigeration system.

Several factors influence the required wall thickness, including:

ACR copper tubing is manufactured in different forms and wall thicknesses. Straight lengths of drawn tubing and annealed coils may have different dimensional specifications, even when they share the same outside diameter.

Consequently, there is no single wall thickness that can be assumed for every ACR tube size.

When evaluating copper tube wall thickness, refer to the applicable tubing standard, published technical dimensional tables, and the requirements of the refrigeration system.

For otherwise identical tubing of the same material, temper, and operating conditions, increasing wall thickness can increase its pressure capacity.

However, pressure ratings cannot be determined by wall thickness alone.

Allowable working pressure depends on several factors, including material properties, manufacturing tolerances, temperature, applicable design standards, and the safety factors used in the calculation.

The system’s allowable pressure may also be limited by components such as fittings, valves, joints, and connected equipment.

Always verify the pressure requirements and ratings of the complete refrigeration assembly rather than relying solely on tubing dimensions.

For help comparing different pressure units, use our Pressure Conversion Calculator for BAR, PSI, and MPa.

Although ACR copper tubing and plumbing copper tubing may look similar, they are not necessarily interchangeable.

One of the most common sources of confusion is the way these products are sized.

ACR copper tubing is typically identified by its nominal outside diameter.

For example, a 1/2″ ACR copper tube has a nominal outside diameter of 0.500″.

Common North American plumbing copper tubing conforming to ASTM B88 is typically identified using nominal sizes.

For example, a nominal 1/2″ Type L plumbing copper tube has an outside diameter of 0.625″, equivalent to 5/8″.

This distinction is especially important when ordering replacement copper tubing, selecting fittings, or reviewing installation specifications.

Copper tubing intended for plumbing should not automatically be substituted for ACR tubing.

Refrigeration applications have specific requirements concerning internal cleanliness, allowable pressure, material properties, and compatibility with refrigerants and refrigeration lubricants.

Any substitution must be evaluated against the system design and applicable standards.

Selecting the appropriate refrigerant tubing size involves more than matching the diameter of an existing connection.

The correct tube size depends on the refrigeration system’s design, operating conditions, and component requirements.

Different refrigerants have different pressure and temperature characteristics.

For example, R744 (CO₂) refrigeration systems operate under substantially different conditions than many conventional HFC and HFO refrigeration systems.

For additional information on CO₂ operating pressures, see NDL Industries’ R744 CO₂ Pressure Temperature Chart and Refrigeration Guide.

Understanding refrigerant properties helps determine the appropriate tubing material, size, and pressure requirements.

Refrigerant line sizing depends on factors such as system capacity, refrigerant mass flow, pressure drop, velocity, line length, and elevation changes.

Liquid, suction, and discharge lines may require different sizing considerations.

For example, an undersized refrigerant line can create excessive pressure drop, potentially affecting system performance and efficiency. An oversized line may create challenges with refrigerant velocity and oil return.

Refrigerant piping design should balance system capacity, refrigerant velocity, pressure drop, and oil return requirements to support efficient operation.

For additional technical guidance, explore the ASHRAE Handbook — Refrigeration, which covers refrigeration system design and related engineering considerations.

Always use the equipment manufacturer’s specifications and an appropriate engineering sizing method to determine the required line diameter.

Ensure the selected copper tubing meets the system’s design pressure and temperature requirements.

Do not assume that all copper tubing with the same outside diameter shares the same allowable working pressure.

Copper fittings must match the tubing’s required outside diameter, connection method, and application.

For example, tubing identified as 7/8″ OD must be paired with a fitting intended for the corresponding tubing size.

Additionally, confirm the fitting’s specified pressure rating, material compatibility, and joining requirements.

Proper installation is essential to maintaining the reliability of the refrigeration system.

This includes using approved joining methods, following manufacturer instructions, protecting tubing from contamination, and performing the required pressure testing and commissioning procedures.

Selecting the correct copper tubing is only one part of establishing a reliable refrigeration piping system.

The fittings connecting those tubes must also be suitable for the system’s pressure, temperature, refrigerant, and installation requirements.

We manufacture ACR copper fittings for HVAC and refrigeration applications, with pressure ratings that vary by fitting size.

Our ACR copper fittings offer:

These fittings provide options for contractors and engineers working across a range of HVAC and refrigeration applications.

By confirming tubing dimensions and fitting compatibility during system design and installation, contractors and engineers can help reduce connection issues and ensure components meet their intended operating requirements.

Explore our ACR Copper Fittings to view our complete product selection, pressure ratings, technical specifications, and available sizes for HVAC and refrigeration applications.

ACR stands for Air Conditioning and Refrigeration. ACR copper tubing is designed for use in refrigerant piping systems and is commonly manufactured to requirements covering dimensions, cleanliness, and material properties.

ACR copper tubing is typically identified by its outside diameter (OD). For example, 3/8″ ACR tubing has a nominal outside diameter of 0.375″, equivalent to 9.525 mm.

The nominal outside diameter of 1/2″ ACR copper tubing is 0.500″, or 12.7 mm. This differs from nominal 1/2″ plumbing copper tubing, which typically has a 0.625″ outside diameter.

A 7/8″ ACR copper tube has a nominal outside diameter of 0.875″, equivalent to 22.225 mm.

Not exactly. ACR identifies tubing intended for air conditioning and refrigeration applications, while Type L refers to a plumbing copper tubing wall thickness designation. Some ACR tubing products have dimensions corresponding to Type L tubing, but their application requirements, cleanliness, and sizing conventions must also be considered.

There is no universal wall thickness for all ACR copper tubing. Wall thickness varies by tube diameter, temper, product specification, and manufacturer. Consult the applicable tubing standard and technical dimensional tables for specific measurements.

Copper tubing suitability for R744 (CO₂) refrigeration must be evaluated against the pressures, temperatures, materials, and applicable design standards of the specific system. Conventional ACR tubing should not be assumed suitable for high-pressure CO₂ applications without engineering verification.

Multiply the outside diameter in inches by 25.4.

For example:

7/8″ = 0.875 × 25.4 = 22.225 mm.

This method can be used to convert any fractional inch outside diameter into its metric equivalent.