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ACR Tube Size Chart (Actual OD vs Plumbing Nominal)

ACR copper tube is named by its actual outside diameter. Plumbing copper is named by a nominal size that is 1/8 in smaller than the OD. This chart lines the two systems up.

Ref HV-0045ASTM B280ASTM B88

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Copper tube for air conditioning and refrigeration (ACR, ASTM B280) is sized by its actual outside diameter. A 7/8 ACR tube measures 7/8 in OD. Plumbing tube (Types K, L and M, ASTM B88) is sized by a nominal size. For plumbing tube, the OD is always the nominal size plus 1/8 in. So 3/4 nominal Type L also measures 7/8 in OD. The two tubes share the same OD, so they take the same wrot fittings. But the fittings and tube are called by different names in each trade.

How to identify

Measure the OD with calipers or a tube gauge. Do not measure the ID.
ACR tube is cleaned and capped at the ends. Hard-drawn straight lengths are often charged with nitrogen. Soft coils are sold by OD.
Check the printed marking. It shows the type and size, and ACR tube is marked ACR.
Fittings sold for plumbing are labeled by nominal size. Convert before ordering for an ACR job.

Size chart

ACR size (actual OD, in)	OD (mm, approx.)	Plumbing nominal with the same OD
1/4	6.35	1/8
3/8	9.53	1/4
1/2	12.70	3/8
5/8	15.88	1/2
3/4	19.05	5/8
7/8	22.23	3/4
1-1/8	28.58	1
1-3/8	34.93	1-1/4
1-5/8	41.28	1-1/2
2-1/8	53.98	2
2-5/8	66.68	2-1/2
3-1/8	79.38	3

Key points

Rule of thumb: ACR size minus 1/8 in equals the plumbing nominal size.
Same OD does not mean same wall. Wall thickness depends on the tube type and temper. Check the standard for the wall and the system's pressure needs.
ACR tube is cleaned for refrigerant service. Plumbing tube is not, and should not go into a refrigerant system without proper cleaning.
Metric tube sizes (for example 6, 10, 12 or 16 mm) are close to some ACR sizes but not identical. Do not mix them without matching fittings.

Common mistakes

Ordering 7/8 plumbing fittings for 7/8 ACR line. The correct plumbing fitting is 3/4 nominal.
Measuring ID and calling it the tube size.
Assuming the pressure rating is the same for every tube with the same OD.

Governing standards: ASTM B280 (ACR tube); ASTM B88 (water tube, Types K, L and M); manufacturer data for wall thickness and ratings; the adopted mechanical code.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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