Display Cable Bandwidth Checker

Bought a shiny 4K 144 Hz monitor and the picture keeps cutting out? The monitor is rarely the problem — the cable is. Every HDMI and DisplayPort version has a hard bandwidth ceiling, and if your resolution times refresh rate times color depth exceeds it, you get a black screen, flicker, or a silently downgraded signal. This checker does the math for you.

Why your cable can be the bottleneck

Video is a stream of pixels, and every pixel carries color bits. Multiply pixels per frame by frames per second by bits per pixel and you get the bandwidth your setup demands. The ceilings are unforgiving: HDMI 1.4 tops out at 10.2 Gbps, HDMI 2.0 at 18, DisplayPort 1.4 at 25.92, HDMI 2.1 at 48, and DisplayPort 2.1 at 80. The cruel part is that old and new cables look identical — nothing printed on the plug reliably tells you the version.

How the bandwidth math works

Bandwidth in Gbps equals width times height times refresh rate times bits per pixel, divided by a billion. Bits per pixel is your color depth multiplied by 3 for full 4:4:4 color, by 2 for 4:2:2, or by 1.5 for 4:2:0. Chroma subsampling is the big lever: 4:2:0, which is what almost all video uses, cuts the requirement in half compared with the full 4:4:4 color your PC desktop prefers.

Worked example: 4K at 120 Hz

Take 3840 by 2160, which is 8,294,400 pixels per frame. At 120 frames per second that is 995,328,000 pixels every second. With 10-bit HDR at full 4:4:4 color you need 30 bits per pixel, so the total is 29.86 Gbps. HDMI 2.0 at 18 Gbps fails, and even DisplayPort 1.4 at 25.92 Gbps falls short — only HDMI 2.1 or DisplayPort 2.1 can carry it. Switch the chroma to 4:2:0, dropping to 15 bits per pixel, and the need falls to 14.93 Gbps, which an ordinary HDMI 2.0 cable handles. That single setting is why game consoles can push 4K 120 Hz through modest cables.

Practical tips before you buy

First, check the ports on your graphics card and monitor, because a cable can never exceed the weakest port in the chain. Second, keep 4:4:4 for PC text and desktop work where sharp edges matter, but accept 4:2:0 for movies and games. Third, look for honest labels: Ultra High Speed means HDMI 2.1, and DP80 means full DisplayPort 2.1. Fourth, keep high-bandwidth cables under 3 meters, since longer passive cables often fail at full speed. Finally, if no cable version fits your numbers, turn on Display Stream Compression in your monitor and GPU settings — it is visually lossless and roughly triples effective bandwidth.