A/C Hose Size Chart: What #8, #10 and #12 Actually Measure in Millimetres

Ask three suppliers what a “#8” air conditioning hose measures in millimetres and you will get three answers: 8 mm, 12.7 mm, and a shrug. All three are defensible. That is the problem.

A/C hose circulates under three different sizing systems at once — the SAE J2064 nominal sizes, the -AN (Army-Navy) dash numbers borrowed from hydraulics, and the millimetre part numbers that factories actually stamp on the tube. They overlap, they do not align, and nobody publishes the reconciliation.

This page does. Below: how each system works, a lookup tool for any inside diameter you measure, the full measured dimensions of 20 production part numbers, and the five mistakes that cause most wrong-size orders.

1. Three systems, one hose

SAE J2064 nominal sizes

The standard works in millimetres with an inch equivalent, and the sequence is not what you would guess from hydraulic hose:

SAE sizes and mean inside diameters from SAE J2064 Table 1. The -AN column is the nearest hydraulic dash size, not an SAE equivalence.

Notice two things. First, the inch fractions include 13/32" — a size that does not exist in the -AN world. Second, the “nominal” number (8, 10, 13, 16, 19) is close to but not identical with the mean inside diameter.

-AN dash numbers

Dash sizes count sixteenths of an inch: #8 means 8/16" = 1/2" = 12.7 mm. This system comes from hydraulic and racing plumbing, and it is the one most American workshops and online retailers use:

Here is the trap. Below about 13 mm, the two systems stop lining up. SAE size 8 (5/16") and SAE size 10 (13/32") have no -AN equivalent at all — #6 is 3/8" (9.5 mm), which falls between them. So when a supplier calls an 8 mm hose “#8”, they are not using the -AN system; they are using the millimetre number and putting a hash in front of it.

Factory part numbers

We, like most manufacturers, stamp the metric size: EA4-080 is an 8.2 mm hose, CA5-130 is 13.2 mm, EA48-222 is 22.2 mm. No conversion, no guessing.

So which is right? Both — but they describe different things. “#8” means 12.7 mm if you are speaking -AN, and roughly 8 mm if you are speaking Chinese or European factory shorthand. This is why the only safe way to order is to give the inside diameter in millimetres and let the supplier map it to their part number.

2. Size lookup tool

Measure the inside diameter, enter it, and the tool returns the closest part numbers with the SAE nominal size and the nearest dash number for reference.

3. Full dimension chart — 20 production part numbers

Measured production dimensions. Note the two rows marked 1.5 MPa — see the warning below.

4. How to measure a hose correctly

1. Measure the fitting, not the hose. The most reliable figure is the outside diameter of the metal insert (the part that goes inside the hose). That is the bore you must match.
2. If you only have the old hose: cut a short piece square, and measure the inside diameter across the cut with a vernier caliper. Take two readings at 90° and average them — hose is rarely perfectly round.
3. Do not measure the outside diameter and subtract a “standard” wall. Wall thickness runs from 3.5 mm to 6.3 mm across our series. On an 8 mm bore that is the difference between a 15.2 mm and a 19.0 mm hose.
4. Check the bend radius before you commit. 55 mm on EA4-080; 135 mm on EA48-222. If the routing needs a tighter turn than the hose allows, you need a different size or a formed assembly.
5. Write the millimetre figure on the order. Not “#8”. “13.0 mm I.D.” ends the conversation in one line.

5. Five mistakes that cause most wrong-size orders

6. Which series for which size

• 8–13 mm — the everyday range. EA4 for standard engine bays, CA5 where you want lower permeation, CA9 where the hose rubs a frame or sits near a hot manifold.
• 15–18 mm — suction and return lines in these series. Check the pressure rating before assuming it can take discharge duty.
• 10.7 / 12.7 / 16.1 / 22.2 mm — refrigerated transport sizes on the EA48 series, which holds 3.5 MPa across the range and is tested with R404a / R410a at +80 °C.
• Anything not listed — assemblies are crimped to your drawing, sample or OE number, and non-standard bores can be produced to order.

7. Ordering notes

• MOQ: 100 meters per size
• Stock: common sizes held in stock; lead time 3–7 days after order confirmation
• Fittings: matched aluminum fittings available; standard A/C crimp machines and dies work on these series
• Still unsure? Send the inside diameter, the refrigerant and whether the run is suction or discharge — we will confirm the part number before you pay.

Related reading and products

• SAE J2064 Explained: hose types A–G, permeation limits and what most suppliers get wrong
• Automotive A/C Hose by the Meter: choosing series, size and barrier class
• EA4 4-layer thin wall A/C hose — 6 sizes, 8.2–18.5 mm
• CA5 5-layer thin wall A/C hose — 5 sizes, 8.2–15.2 mm
• CA9 5-layer thick wall A/C hose — heavy wall for abrasion duty
• EA48 refrigerated truck hose — 6 sizes, 8.2–22.2 mm, 3.5 MPa throughout
• Custom crimped A/C hose assemblies — built to drawing or OE number