How does AWG relate to HDMI cables?

This most commonly found viewpoint on the subject is that “the lower the cable AWG rating, the better the cable is”. As with most factors that relate to HDMI cable performance this notion is extremely over-simplified, but is in the main correct.

It is important to use non-ambiguous terminology when talking about HDMI cables. We must remember that it is not a ‘performance’ issue, it is simply whether or not the cable will pass the signal sufficiently within certain tolerances in order for the display to decode and show an image. There is no differing in picture quality, the images will either show up in 100% picture perfection or it won’t.

Now it is true to say that a 24 AWG rated cable has a far greater chance of passing the signal sufficiently well enough for the image to be displayed than a 28 AWG rated cable for example.

So why is AWG important then?

AWG rating becomes important when we start to consider HDMI cable length. Generally speaking any HDMI cables under 4 metres in length will pass a 1080p 60hz signal sufficiently and perfectly well enough to show a rock-solid 1080p image if 28 AWG or lower, possibly even 30 AWG with some devices.

As the cable length increases, so must the cable AWG decrease to offer a greater possibly of the cable being able to pass the 1080p image data. At 5 – 7 metres, cables will probably at least require at least 26 AWG and lengths over 7 metre 24 AWG.

Want to get more technical about AWG?

Fundamentally the most important attribute of any AV cable is its characteristic impedance. The cable used in the construction of HDMI cables is not like most AV cables we are used to, the coaxial cable of old. HDMI cabling is constructed using something called twisted pairs. Because of this cable’s make-up characteristic impedance is much harder to control and is liable to change significantly from one inch to the next.

Because of the extreme frequencies that a HDMI signal runs at, there is essentially no signal flowing through the middle of an HDMI cable conductor, it is all skimming the surface. In cables using lower frequencies the size of the cable diameter has much more importance, this is because the lower frequencies travel much deeper and throughout the cable conductor, not just ‘skin-deep’ around the perimeter like the high frequencies of HDMI.

Because of the way that HDMI signals only travel skin deep in the cable conductor, the way we measure the real-world resistance relative to HDMI signals has to alter. The cross-sectional area normally used for resistance measurement is practically irrelevant because the "skin depth" is next to nothing. Instead of cross-sectional area, loss to resistance is going to be inversely proportional to the amount of copper through which the signal actually passes. That is, it's going to be inversely proportional to the cable's surface area, or, speaking in cross-sectional terms, its perimeter. A 24 AWG wire has a diameter of .0201 inch, and a 22 AWG wire has a diameter of .0253 inch. Since the perimeters are simply these numbers each multiplied by pi, we can see the ratio of perimeters without doing that multiplication. The 22 AWG is "bigger" than the 24 by .0253/.0201, or a factor of 1.259. When we were concerned with area of the cross-section rather than perimeter, the ratio of circular mils was much steeper: 640.4/404, making the 22 AWG "bigger" by a factor of 1.585. Instead of the use of 22 AWG dropping resistance to about 63% of the 24 AWG wire's resistance, as happens at DC, when looking at a the real-world effect on a HDMI signal it drops resistance only to about 80% of the 24 AWG's value.

Of course, technically speaking any reduction in resistance is good; the point here is simply to show that it isn't as good as one might expect. If all else were equal, one would expect 22 AWG HDMI cable to be useful for a distance of about 20% longer than a similar 24 AWG cable (this almost certainly overstates the advantage, because, of course, all else isn't equal. The longer run will show greater performance losses from other factors, including capacitance, crosstalk, skew and return loss). Real-world distance advantage may only be 15% over 24 AWG.