Yes — you need a certified Ultra High Speed HDMI cable for reliable 4K 120Hz. It supports up to 48Gbps, which is the minimum bandwidth required for uncompressed 4K@120Hz with HDR and VRR under HDMI 2.1.
- You use a certified Ultra High Speed HDMI (2.1) cable
- Both your source device and display support HDMI 2.1 at 48Gbps
- Cable length is 3 metres or under
- You use an older Premium High Speed cable (18Gbps max)
- Your cable is uncertified and labelled “HDMI 2.1” without testing
- Cable exceeds 3 metres or has poor signal integrity
What Makes an Ultra High Speed HDMI Cable Different?
HDMI cables are grouped into certified speed tiers. The Ultra High Speed tier is the only one rated for 48Gbps, which is what HDMI 2.1 needs for 4K at 120Hz without compression. Older Premium High Speed cables top out at 18Gbps — enough for 4K@60Hz, but not 4K@120Hz in full quality.
The certification matters more than the label. Many cheap cables are printed with “HDMI 2.1” but have never been tested. They often drop signal, show flickering, or fall back to a lower resolution when pushed to high refresh rates.
What Bandwidth Does 4K 120Hz Actually Need?
Uncompressed 4K@120Hz with 4:4:4 colour and HDR requires close to 48Gbps. Here is how the main setups compare:
| Setup | Works? | Need | Note |
|---|---|---|---|
| 4K 60Hz HDR | Yes | Premium High Speed (18Gbps) | Older cable is fine here |
| 4K 120Hz SDR (compressed) | Sometimes | Premium High Speed | Uses DSC; quality reduced |
| 4K 120Hz HDR uncompressed | Yes | Ultra High Speed (48Gbps) | Requires HDMI 2.1 cable and ports |
| 4K 144Hz | Yes | Ultra High Speed (48Gbps) | TV/monitor must also support it |
Your Device and Display Must Also Support HDMI 2.1
The cable is only one part. Your source — such as a PS5, Xbox Series X, or a PC with a modern GPU — and your TV or monitor must both have HDMI 2.1 ports capable of 48Gbps. If either end is limited to 18Gbps, you will not get 4K@120Hz regardless of the cable you use.
If you are connecting via USB-C, the rules change. See our guide on whether USB-C can connect to HDMI to understand which adapters carry the full bandwidth.
Cable Length Matters Too
Ultra High Speed cables are rated for full 48Gbps performance up to 3 metres. Beyond that, signal integrity can degrade and cause dropouts or automatic resolution downgrading. If you need a longer run, look for active Ultra High Speed cables designed for extended lengths.
For setups where video is carried over USB-C instead of HDMI, also check whether your USB-C cable supports video output before assuming it will handle high refresh rates.
How to Confirm Your Cable Is Certified
Look for the HDMI Forum’s official Ultra High Speed cable certification mark on the packaging. You can also check the cable with the HDMI Cable Certification app by scanning the QR code printed on certified cables. If there is no QR code, treat the cable as uncertified.
- Look for the cable certification label on the box
- Scan the QR code with the HDMI Cable Certification app
- Avoid unbranded cables with no verifiable test data
Bottom line: An Ultra High Speed HDMI cable is essential for 4K 120Hz — but only works if your source device and display both have HDMI 2.1 ports. Buy a certified cable under 3 metres and verify the label to avoid signal issues and wasted money.