Quick Answer: Identify a cable by three things: the print on the jacket, the certification label, and what it actually carries. Look for High Speed (10.2 Gbit/s, 1080p), Premium High Speed (18 Gbit/s, 4K60) or Ultra High Speed (48 Gbit/s, 8K60), plus the AWG figure and any arrow marking an active cable. If the print has worn off, test it: 1080p60 needs 4.45 Gbit/s, 4K60 needs 17.8 Gbit/s, and a cable that fails at 4K but passes at 1080p is a High Speed part.
Nearly every HDMI cable looks identical, and the jacket print is the only label most of them ever carry. Three tests settle the question without a meter: read the print, check for a certification label, and push a known format through it. Everything else, including connector colour, is decoration.
Reading the jacket print
Good cable is printed every 12 in (300 mm) with the rating, the conductor gauge and often the word Ethernet. The gauge matters as much as the rating: 30 AWG is a short-run part limited to about 6 ft (1.8 m) at 18 Gbit/s, 24 AWG holds 4K60 to roughly 25 ft (7.6 m), and 22 AWG reaches 50 ft (15 m) only with equalisation built into the plug.
The three official ratings
High Speed is rated for 10.2 Gbit/s, enough for 1080p60 and 4K30. Premium High Speed guarantees 18 Gbit/s and is tested per unit, which is what 4K60 at 8-bit 4:4:4 needs. Ultra High Speed guarantees 48 Gbit/s for 4K120 and 8K60. A cable sold as 4K without any of these words is a claim, not a rating.
Certification labels and codes
Premium and Ultra High Speed assemblies carry a label with a QR code that resolves to a test record for that serial number. Scan it before trusting a long run. A label without a scannable code, or a code that returns nothing, is the single most reliable sign of a cable that has never been tested at its claimed rate.
Testing what it actually carries
Set the source to a known format and watch whether the link holds for 10 minutes. Use 4K60 at 8-bit 4:4:4 for 17.8 Gbit/s, then 8K60 for 48 Gbit/s if the hardware allows. A link that renegotiates down to 4K30 or drops audio is failing at the rate, not at the resolution.
Active versus passive
An active cable has a chip in the source-end plug and is directional, marked with arrows or labelled Source and Display. It is the only way past about 25 ft (7.6 m) at 18 Gbit/s. Plugged backwards it usually shows nothing at all, which is often mistaken for a dead cable.
Ratings compared
| Marking | Bandwidth | Top format | Passive length | Test format |
|---|
| Standard | 4.95 Gbit/s | 1080i60 | 50 ft (15 m) | 1080i |
| High Speed | 10.2 Gbit/s | 4K30 | 50 ft (15 m) | 1080p60 |
| Premium High Speed | 18 Gbit/s | 4K60 | 25 ft (7.6 m) | 4K60 4:4:4 |
| Ultra High Speed | 48 Gbit/s | 8K60 | 10 ft (3 m) | 4K120 |
| No marking | Unknown | Assume 1080p | Unknown | 1080p60 |
Practical scenarios
- Situation: A box of unmarked leads sits in a store room. Test each at 1080p60 and label it with a wrap of tape: 10 minutes of work sorts the pile into Standard, High Speed and unknown at no cost.
- Situation: A 4K display runs at 4K30 with a cable from 2012. The link is negotiating down because the part is High Speed at 10.2 Gbit/s; a Premium High Speed lead restores 4K60.
- Situation: A camera needs 25 ft (7.6 m) at 4K60 and the passive lead flickers. That is the edge of the 18 Gbit/s budget: fit an active cable with the arrows at the source end, or a 50 ft 4k hdmi cable with equalisation.
- Situation: An 8K display shows a blank screen on an older lead. Only a certified 8k hdmi cable at 48 Gbit/s will lock the link; no adapter rescues a 10.2 Gbit/s part.
Recommendation and failure symptoms
Label every installed cable at both ends with its rating and the date; a strip of tape takes 10 seconds and saves an hour of fault-finding. Where the print has gone, treat the lead as 1080p until a 4K60 test passes. A hdmi cable that fails at 4K60 but holds 1080p60 is at its rated ceiling, not faulty. Symptoms worth recognising: sparkles that increase with resolution mean margin, not damage; a picture that appears after 5 seconds and then drops means the equaliser is at its limit; audio that cuts while video holds means the data islands are being lost, which happens first on long passive runs; and nothing at all on a long lead usually means an active cable is plugged in backwards.
FAQ
Can a cheap cable damage a display?
No. A failing cable produces no picture or an unstable one, but it does not damage the ports. The risk is mechanical: an oversized plug shell or a bent connector can strain the socket, so check the fit rather than the price.
Does a thicker cable always mean higher bandwidth?
Not reliably. Gauge affects attenuation, but shielding, dielectric and how the pairs are twisted matter as much. A 24 AWG High Speed lead is thicker than a 30 AWG Premium High Speed lead and slower at 4K60.
What do the arrows on a long cable mean?
They mark an active cable and show which end goes to the source. The plug with the chip must be at the player or computer, and the display end is passive. Reversing them normally gives no picture at all.
