Upgrading to a 4K 144 Hz monitor, or plugging a gaming PC into a new television, is supposed to be the easy part. You unbox the screen, plug in the cable that came in the box, and expect the full advertised experience. Then the picture flickers, the screen goes black for a second every few minutes, or the refresh-rate menu stubbornly refuses to offer the number printed on the box. The monitor is rarely the problem. The cable is — or, more precisely, the amount of bandwidth the cable version can carry.
HDMI and DisplayPort cables are digital: they either carry your signal or they do not. But every version of each standard has a hard bandwidth ceiling measured in gigabits per second (Gbps), and once your resolution, refresh rate, and color depth demand more than that ceiling allows, the link degrades — silently dropping the refresh rate, switching to chroma subsampling, or dropping the picture entirely. This guide explains the math, compares every current standard, and shows how to pick a cable that fits your setup on the first try.
Why the cable can be the bottleneck
Video is a stream of pixels, and each pixel carries color information. Multiply the pixels in a frame by the number of frames per second by the bits of color each pixel carries, and you get the bandwidth your setup demands. Because nothing on the cable itself reliably announces its version — old and new cables look identical — it is easy to run a modern display through an ancient link. A ten-year-old HDMI cable from a drawer will happily carry 1080p at 60 Hz and fail spectacularly at 4K 120 Hz, with no visible clue why.
The failure modes are frustratingly indirect. Some displays downgrade the signal without telling you, delivering 4K at 60 Hz instead of the 120 Hz you paid for. Others flicker or cut to black when the bitrate peaks during bright, fast scenes. In the worst cases, the display simply shows "no signal." All of these can look like a broken monitor or a weak graphics card, which is why the cable deserves to be checked first.
The bandwidth formula, in plain English
Three variables decide how much bandwidth a video signal needs: how many pixels each frame holds (resolution), how many frames are sent per second (refresh rate), and how much color data rides with each pixel (color depth and chroma subsampling). The relationship is linear, so doubling any one of them doubles the total.
Bandwidth (Gbps) = width × height × refresh rate (Hz) × bits per pixel ÷ 1,000,000,000 — where bits per pixel = color depth × 3 for full 4:4:4 color, × 2 for 4:2:2, or × 1.5 for 4:2:0.
Chroma subsampling deserves a special mention because it is the biggest lever you have. Human vision is far more sensitive to brightness detail than to color detail, so video formats routinely store color at half resolution (4:2:0). That single setting cuts the bandwidth requirement in half compared with the full 4:4:4 color a PC desktop prefers for razor-sharp text.
HDMI and DisplayPort ceilings, side by side
Five standard versions cover essentially every cable sold today. Memorizing these numbers makes every cable-buying decision easy:
| Cable standard | Max bandwidth | Typical ceiling in practice |
|---|---|---|
| HDMI 1.4 | 10.2 Gbps | 4K at 30 Hz |
| HDMI 2.0 / 2.0b | 18.0 Gbps | 4K at 60 Hz |
| DisplayPort 1.4 | 25.92 Gbps | 4K at 120 Hz with light compression |
| HDMI 2.1 | 48.0 Gbps | 4K at 120 Hz uncompressed, 8K at 60 Hz compressed |
| DisplayPort 2.1 | 80.0 Gbps | 8K at 60 Hz uncompressed, high-refresh 4K |
Two honest labels tell you what you are actually buying: "Ultra High Speed" means HDMI 2.1, and "DP80" means full-bandwidth DisplayPort 2.1. Beware of vague "4K cable" marketing — a cable advertised for 4K usually only promises 4K at 30 Hz.
Worked examples: what common setups actually need
Running the numbers for typical configurations shows where each standard breaks down:
| Setup | Bandwidth needed | Minimum cable |
|---|---|---|
| 1080p, 60 Hz, 8-bit SDR | ~3.0 Gbps | HDMI 1.4 |
| 1440p, 144 Hz, 8-bit | ~12.7 Gbps | HDMI 2.0 |
| 4K, 60 Hz, 10-bit HDR (4:4:4) | ~14.9 Gbps | HDMI 2.0 |
| 4K, 120 Hz, 10-bit HDR (4:4:4) | ~29.9 Gbps | HDMI 2.1 or DisplayPort 2.1 |
| 4K, 120 Hz, 10-bit HDR (4:2:0) | ~14.9 Gbps | HDMI 2.0 |
| 8K, 60 Hz, 10-bit HDR (4:4:4) | ~59.7 Gbps | DisplayPort 2.1 |
The 4K 120 Hz pair of rows is the instructive one. At full 4:4:4 color the signal needs 29.9 Gbps — beyond even DisplayPort 1.4's 25.9 Gbps — so only HDMI 2.1 or DisplayPort 2.1 works. Switch the chroma to 4:2:0 and the requirement halves to 14.9 Gbps, which an ordinary HDMI 2.0 cable carries. That is why game consoles push 4K 120 Hz through modest cables: they trade a little color resolution, which the eye barely notices in motion, for a dramatically smaller pipe.
Three settings that change the number
Before buying a new cable, check whether a settings change solves the problem:
- Color depth. Dropping from 10-bit HDR to 8-bit SDR cuts the per-pixel data by a fifth. Keep HDR where it matters, but know it has a bandwidth cost.
- Chroma subsampling. 4:4:4 matters for PC desktop work, where sharp colored text edges show the difference. For movies and games, 4:2:0 is visually near-identical and halves the load.
- Display Stream Compression (DSC). Built into DisplayPort 1.4 and later and HDMI 2.1 devices, DSC is a visually lossless compression standard that roughly triples effective bandwidth — it is how 8K at 60 Hz works over cables that cannot carry it raw. Enable it in your monitor and GPU settings when no cable version fits.
Five rules for buying the right cable
- The weakest link wins. Check the ports on your graphics card and your monitor first — a cable can never exceed the slowest port in the chain.
- Buy the certified version, not the brand. Digital signals either fit or they do not; a cable that meets your bandwidth number delivers a perfect picture, and a pricier one adds nothing.
- Match the label to the version. "Ultra High Speed" means HDMI 2.1; "DP80" means full DisplayPort 2.1. "4K cable" usually means 4K at 30 Hz.
- Keep it short. Long passive cables fail at full speed more often than short ones — for high-bandwidth runs, stay under three meters or switch to active or fiber cables.
- Do the math before you shop. Run your resolution, refresh rate, and color depth through a bandwidth checker so you buy the cheapest version that fits — once.
Try it now: Display Cable Bandwidth Checker — enter your resolution, refresh rate, and color depth to see exactly which HDMI or DisplayPort version your setup needs.
Frequently asked questions
Does a more expensive HDMI cable give a better picture?
No. A digital signal either fits through the cable or it does not, so a cable that meets your bandwidth number gives a perfect picture and a pricier one adds nothing. Pay for the certified version, not the brand.
What is Display Stream Compression (DSC), and when do I need it?
Display Stream Compression is a visually lossless compression standard built into DisplayPort 1.4 and later and HDMI 2.1 devices. It roughly triples effective bandwidth, which is how 8K at 60 Hz works over cables that cannot carry it raw. Enable it in your monitor and graphics card settings when no cable version fits your numbers.
Can I use an adapter between HDMI and DisplayPort?
Usually, yes — but the adapter is limited to the lower of the two standards, and direction matters: most inexpensive adapters only convert a DisplayPort output to an HDMI input, not the reverse. For high-bandwidth setups, use an active adapter rated for your target speed.