What is 4K? The basics of Ultra HD explained

4K resolution TV mounted on a wall showing action scene
(Image credit: Panasonic)

The TV tech term 4K describes an ultra high-definition screen resolution. You might also see this labelled as UHD, 4K or 4K UHD depending on which brand makes the TV. But they’re all talking about the same thing.

Right now, 4K has overtaken both HD and full HD to become the most popular TV resolution of choice for all major TV brands. You’ll find the 4K screen resolution in most of today’s TVs – except some small TVs, which tend to cap out at Full HD resolution – as well as most PC monitors.

The important thing to know here is that just because you’ve got a 4K TV doesn’t mean you need to have lots of 4K TV shows and movies. That’s because many of the best 4K TVs are able to display lower-resolution images. This means your favorite TV shows and movies that have been filmed in HD will play like they’re meant to on a 4K display regardless – some might even be upscaled by your TV, which means they’re improved to ensure they look normal on a 4K screen. 

The brilliant resolution offered by a 4K TV could tempt anyone into upgrading their non-4K TV. But there are other new kinds of technology inside many of the best 4K TVs that are also worth finding out more about. They could make an upgrade a must-have rather than a nice-to-have. These features include Quantum Dot and OLED panels, as well as High Dynamic Range (HDR), but they vary from model to model.

In the guide below, you'll find a video explaining the basics of 4K, along with all of the information you need to know about pixel count, viewing distances, and the difference 4K really makes to your viewing experience. 

What is 4K resolution?

We know it's seriously upgraded our viewing experience, but what is 4K? 

4K resolution, at least the way most TV companies define it, is 3840 x 2160 pixels, or 2160p. To put that in perspective, a Full HD 1080p image is only 1920 x 1080. 4K screens have about 8 million pixels, which is around four times what your current 1080p set can display.

Think of your TV like a grid, with rows and columns. A full HD 1080p image is 1080 rows high and 1920 columns wide. A 4K image approximately doubles the numbers in both directions, yielding approximately four times as many pixels total. To put it another way, you could fit every pixel from your 1080p set onto one-quarter of a 4K screen.

A man in a chair watching a Samsung QN95A Neo QLED TV in a living room

(Image credit: Samsung)

Why is it called 4K?

It's called 4K because the images are around 4,000 pixels wide. And before you ask, yes, the industry named 1080 resolution after image height, but named 4K after image width. For extra added fun, you also might hear this resolution referred to as 2160p. Welcome to the future. It's confusing here.

Do all of those extra pixels matter?

That's where it gets sticky. We're talking about a similar jump in resolution as the one from SD (480 lines high) to HD (1080 lines high). And 4K screens are noticeably sharper than 1080p screens. 

But if you're sticking with roughly the same size of television, and are used to sitting pretty close, you may not see that much of a difference – especially if you're still mostly watching HD content rather than 4K video.

How close do I need to sit to a 4K screen?

Remember when Apple made a big fuss about "retina" displays a few iPhones back? "Retina" refers to screens that have sufficient resolution that at a normal viewing distance your eye can't make out individual pixels. Get far enough away from a 1080p set and, hey presto, it's a retina display! 

More importantly, at that same distance, your eyeballs won't be able to squeeze any more detail out of a 4K image than a 1080 one. If you're at "retina distance" from your 1080p set now and don't plan on moving your couch closer, upgrading to 4K may not make a big difference to your experience. This chart shows how close you need to sit at any given screen size to see the difference.

Actor in Jupiter's Legacy

If you have the bandwidth, you can now watch many of Netflix's shows in 4K Ultra HD (Image credit: Netflix)

4K vs UHD: what's the difference?

Technically, "Ultra High Definition" is actually a derivation of the 4K digital cinema standard. However while your local multiplex shows images in native 4096 x 2160 4K resolution, the new Ultra HD consumer format has a slightly lower resolution of 3840 x 2160.

This is one reason why some brands prefer not to use the 4K label at all, sticking with Ultra HD or UHD instead. However, the numerical shorthand looks likely to stick.

Why should I care about 4K Ultra HD?

There are many reasons why 4K should make you rethink your next TV purchase (actually, there are eleven and you can read about them here), not all of them immediately obvious.

Photographers who routinely view their work on an HD TV are seeing but a fraction of the detail inherent in their pictures when they view them at 2160p.

An Ultra HD display reveals so much more nuance and detail – the difference can be astonishing. While 3D has proved to be a faddish diversion, 4K comes without caveats. Its higher resolution images are simply better.

The higher pixel density of a 4K panel also enable you get much closer without the grid-like structure of the image itself becoming visible –this means you can comfortably watch a much larger screen from the same seating position as your current Full HD panel.

My friend told me about 4K OLED. What's that?

More acronyms! Isn't this fun? OLED – organic light emitting diodes – have been around for some time, but producing big screens using this technology has proven to be prohibitively expensive, something which has so far prevented OLED television from being a mainstream proposition.

It's a real shame because OLED technology can be stunning, offering vibrant colors, deep blacks and bright whites. But don't give up hope just yet. Several companies (most prominently LG) are laboring away to bring OLED to 4K televisions. They're certainly gorgeous, though pricing remains high even years after they first came to market – and it's generally accepted that they don't have the longevity of LCD screens.

OLED TVs are improving year on year, though, with reduced risk of burn-in and a new 48-inch size looking to make flagship OLED sets that little bit more affordable to average wallets. 

Read more: What is OLED?

LG A1 OLED showing green tree on display, sitting on white countertop

(Image credit: LG)

Is Netflix in 4K?

Yes – if you pay for it.

Netflix has tiered pricing plans, with 4K films and TV shows becoming available on the Premium tier. Not everything on the service will jump in resolution, though there's a decent amount of Ultra HD content available – including Dark, Star Trek: Discovery, Altered Carbon, and much more. The selection might be more limited than the amount of HD content, but it's increasing day by day. 

Netflix isn't an outlier, either. Amazon has gotten into the 4K UHD streaming game by offering some of its highest-rated shows – Transparent, Mozart in the Jungle, Man in the High Castle, The Grand Tour and Mad Dogs – in Ultra HD.

You'll also find Ultra HD content on Disney Plus, Hulu, Rakuten TV, and other TV streaming services like them – everybody's doing it! Not that some services allow 4K streaming for all subscribers, such as Disney Plus, rather than Netflix's tiered model.

Are 4K and HDR the same thing?

No. There's no shortage of acronyms in home entertainment, and it can certainly get confusing though.

HDR, or high dynamic range, essentially increases the difference between the lightest and the darkest portions of an image. Blacks get properly dark rather than milky grey, and whites get blindingly light.  

This means that images have more depth to them, and you should also be able to perceive more detail in the lightest and darkest portions of the image. 

Netflix was the first content provider to release HDR video in 2015, but Amazon Prime Video also offers high dynamic range content. HDR has also been included in the new Ultra HD Blu-ray standard. You can read our full explainer on High Dynamic Range here.

A LG C1 OLED in a dark living room

(Image credit: LG)

Why isn't broadcast TV all in 4K?

Because every 4K frame contains four times the information of HD, 4K content is four times more bulky than regular HD content in terms of its raw file size. That makes it a challenge to get it to you.

Steps are being made to get 4K content into broadcast television. In the UK, Sky has started broadcasting select sports in 4K, and BT is also using IPTV technology to do likewise

On the streaming side, bandwidth is a definite issue. The internet's bandwidth is already dominated by Netflix's traffic, prompting ISPs to go after them for extra cash, and that's with most of its streams at SD and HD levels. Upping everything to 4K doesn't sound like a reasonable option just yet. 

Even if it were possible to stream 4K content to everyone without breaking the internet, streaming 4K content requires a 25Mbps or faster downstream internet connection, which is faster than most people have at the moment.

A still of a boy in a yellow coat from the Netflix show Dark

Dark (Netflix)

What about gaming in 4K?

4K gaming has been available on PCs for a while before consoles, but the more advanced versions of Sony and Microsoft's gaming machines can now certainly compete.

Sony got the ball rolling with the PS4 Pro, which uses an advanced form of upscaling to generate a 4K image. It might not be native 4K, but we think the results are excellent. 

Although Microsoft dipped its toe in the 4K water with the similarly upscaling Xbox One S, things got serious with the release of the Xbox One X – a powerhouse console which offers native 4K resolution on a handful of titles. 

You can now get even more advanced 4K gaming on next-gen consoles, including the Xbox Series X and PS5, both of which support native 4K at frame rates of up to 120Hz (if the game supports it too, that is). Some recent big video games available in 4K on various platforms include Red Dead Redemption 2, Marvel's Spider-Man and God of War, as well as many others.

We're even hearing rumors of a 4K-ready Nintendo Switch 2 console, too, though since the announcement of the Switch OLED it's likely we don't see an Ultra HD model until at least 2023.

What kind of cables will I need for 4K?

The two standard cables you're most likely to use are either a standard HDMI, or if you're connecting a PC to a Ultra HD monitor, DisplayPort.

HDMI cables now come in four flavors: high speed with ethernet; high speed without ethernet; standard speed with ethernet and standard speed without ethernet. Standard speed cables are capable of 1080i, but aren't able to handle the bandwidth of 4K. High speed cables can do anything higher than 1080i.

Now, as long as you're using the same class of cable, there is no distinguishable difference in terms of performance between one manufacturer's set of cables and another's.

The speed of your connection, however, will depend on the types of connectors. HDMI 1.4 connectors support a 3820x2160-resolution at 30 frames per second (fps), while HDMI 2.0 can output video at Ultra HD resolution at 60 frames per second, and HDMI 2.0a is capable of HDR.

The latest spec, HDMI 2.1, goes that bit further with 4K at 120fps, or 8K at 60fps.

The bottom line is that if your HDMI cable is able to handle 1080p (the standard for a number of years now) then it should be able to also do 4K. Don't get conned into buying expensive cables. 

The other type of cable you can use is DisplayPort. DisplayPort carries 4K image and audio signal from most high-end graphics cards to monitors without any noticeable artifacts or delays.

A still from the PS4 game God of War

PS4 games like God of War offer incredible detail in 4K

Do I need 4K resolution yet?

This question is made harder by the fact that so few TVs aren't 4K these days. While the benefits of 4K are harder to see on smaller sets, it makes little sense not to get a 4K screen given how freely they're available.

For 32-inch TVs, you'll only be expecting Full HD resolution still, as you wouldn't really be able to see much difference with a 4K screen at that size. For 40-inch TVs, though, that benefit is clearer – if not as clear as larger 55-inch, 65-inch, or 75-inch sizes – and you'll now see a lot of the more premium TV technologies at the 40- or 43-inch size.

The Panasonic HX800 features broad HDR format support, with Dolby Vision and HDR10+ as well as HLG (hybrid log gamma), alongside an excellent picture quality, despite being a mid-price LED set. Designer TVs like Samsung The Frame TV, too, are also coming to highly compact sizes, meaning that small doesn't necessarily mean cheap anymore.

One issue to consider is brightness, though. Most 40-inch screens won't have the lighting array needed to really make those pixels shine in HDR – given it needs around 1,000 nits for its intended impact.

What's next for 4K resolution?

4K has cemented itself as a must-have TV capability, and is no longer the reserve of those with serious cash to burn – that's now 8K resolution.

We don't expect to see 4K come to smaller screens than we're seeing already, simply because you can't see the benefit on 24-inch or 32-inch screens at a regular viewing distance.

The main changes and improvements for 4K TVs in the years to come will be on other, related technologies like HDR. Panel technologies continue to shift and compete, too, with OLED and QLED battling it out for dominance, and MicroLED and mini-LED starting to rear their head in premium sets. 

The next challenge for 4K resolution, then, isn't around more pixels so much as better pixels – with better underlying technology and better processing to really make 4K pictures shine.

Nick Pino

Nick Pino is Managing Editor, TV and AV for TechRadar's sister site, Tom's Guide. Previously, he was the Senior Editor of Home Entertainment at TechRadar, covering TVs, headphones, speakers, video games, VR and streaming devices. He's also written for GamesRadar+, Official Xbox Magazine, PC Gamer and other outlets over the last decade, and he has a degree in computer science he's not using if anyone wants it.