100 bandwidth cells — 4K at 120 Hz does not fit through HDMI 2.0
What a display must push each second is its pixel count times the refresh rate times the bits per pixel. Every meeting of 10 resolutions and 10 refresh rates is worked out and checked against six published interface limits.
4K (3840×2160) 120Hz · 23.89 Gbps
- HDMI 1.48.16 Gbps · 292.7%too much
- DisplayPort 1.217.28 Gbps · 138.2%too much
- HDMI 2.014.4 Gbps · 165.9%too much
- DisplayPort 1.425.92 Gbps · 92.2%fits
- HDMI 2.142.67 Gbps · 56%fits
- DisplayPort 2.177.37 Gbps · 30.9%fits
It comes from one multiplication
Width × height × refresh rate × bits per pixel. At 8-bit colour each pixel carries eight bits of red, green and blue, so 24 in total. 4K at 60 Hz is 3840 × 2160 × 60 × 24 = 11.9 Gbps; at 120 Hz it is exactly double, 23.9 Gbps.
The headline number is not all usable
Of HDMI 2.0’s 18 Gbps, video gets 14.4. The link ships eight bits inside ten (8b/10b). HDMI 2.1 packs sixteen bits into eighteen, DisplayPort 2.1 packs 128 into 132. This table therefore compares against the usable video share, not the headline figure.
Borderline cases are not called a pass
A real signal does not carry only the visible pixels: blanking intervals sit between lines and between frames, and in current timings they add about 5 %. So when a figure lands above 95 % of a limit it is marked borderline rather than a pass — that is the range where cable quality and specific hardware start to decide.
Compression changes the answer
Display Stream Compression cuts the payload to roughly a third and the standards call it visually lossless. These figures assume no compression, so a combination marked as too much will often work anyway if both ends support DSC — support varies by device.
A new cable alone may not do it
The bandwidth you get is the narrowest of three: source, display, and cable. A graphics card that speaks HDMI 2.1 still stops at 2.0 if the monitor input is 2.0. For the cable itself, look at the certification tier rather than a version number — Ultra High Speed for HDMI, DP80 and similar for DisplayPort.
Find it by resolution and refresh rate
Data per second (8-bit)
720p (1280×720)
FHD (1920×1080)
UW (2560×1080)
QHD (2560×1440)
UWQHD (3440×1440)
UW (3840×1600)
4K (3840×2160)
5K2K (5120×2160)
5K (5120×2880)
8K (7680×4320)
How to read this
- Data per second = width × height × refresh rate × bits per pixel (24 at 8-bit).
- The comparison is against the usable video share, not the headline bandwidth.
- Above 95 % of a limit it is marked borderline, since blanking can push it over.
- These figures assume no DSC. With compression the payload drops to about a third.
Frequently asked questions
Q. What do I need for 4K at 120 Hz?
23.9 Gbps, which HDMI 2.0 cannot carry at 14.4. You need HDMI 2.1 or DisplayPort 1.4.
Q. Is HDMI 2.0 not 18 Gbps?
That is the total. Video gets 14.4 because the link ships eight bits inside ten.
Q. Is DisplayPort 1.2 better than HDMI 2.0?
On bandwidth alone, yes: DP 1.2 gives video 17.28 Gbps against 14.4 for HDMI 2.0.
Q. Why does 8K 60 Hz rarely work?
It needs 47.8 Gbps, past even HDMI 2.1’s 42.7. That leaves DisplayPort 2.1 or compression.
Q. Is a new cable enough?
No. The limit is the narrowest of source, display and cable.