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What is 4K resolution? Our guide to Ultra HD viewing

What is 4K resolution? Our guide to Ultra HD
(Image credit: Hisense)

4K Ultra HD, which is also known as 'Ultra High Definition' or simply '4K', is the way we describe the super eye-popping resolution found on 4K TVs.

Nowadays, 4K is the most common resolution for brand new televisions. 4K has surpassed the likes of HD and Full HD, which means it's become the go-to pixel resolution for those looking for crisp and detailed TV pictures. 

You'll see the term all over in-store televisions, and certainly in a lot of our TV reviews here at TechRadar. However, 4K isn't the only top TV tech option these days. 4K now has competition in the 8K resolution utilized in 8K TVs, which is an even sharper resolution that's starting to gain traction in the TV market – but, for now at least, 4K still reigns supreme.

However, what's important here is separating the vague hype around 4K from the clear, hard facts. That’s why it's fitting this 4K guide will bring the latter into sharper clarity for you.

You won't get 4K on small TVs, for one – it's saved for 40-inch TVs and above, so you shouldn't go around looking for it on sizes smaller than that. 4K TVs can also display lower-resolution content, such as that filmed in HD, but will 'upscale' to ensure it looks normal on a 4K screen. Upscaling is better on some TVs than others, though, and cheaper sets can struggle to do this well.

However, it might not be the raw resolution of 4K that ends up tempting you into your next TV purchase. Instead, the other cool technologies that are built-in, which include High Dynamic Range (HDR), Quantum Dot and OLED panels, might be what sways your purchasing decision in the end. 

But what is 4K, exactly? How many pixels are we really talking about? And what difference does it make to your viewing experience?

Below you'll find a video outlining 4K in a nutshell, with more information about pixel count, viewing distances, and the difference 4K really makes below that.

UPDATE: If you're on the lookout for a new TV at the moment, then be sure to check TechRadar for all of the biggest and best discounts during the Black Friday and Cyber Monday sales. It's never possible for us to say exactly which devices will be included in the sales, but there's a good chance some high-end TVs will be getting significant price cuts.

What is 4K resolution?

4K resolution, at least the way most TVs 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.

Why is it 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.

What is 4K?

Samsung's new QLED TVs are 4K HDR with insanely high peak brightness levels of up to 2,000 nits

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.

What is 4K?

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

Difference between Ultra HD and 4K

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.

A 4K 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.

What is 4K?

4K UHD screens provide far more detail than HD sets

What is Ultra HD Premium?

If you're sitting there thinking that all these new technologies and acronyms sound confusing, you'd be right. That's why a group of companies decided to form the UHD Alliance with the expressed aim of defining what technologies should be included in the next generation of TV sets.

The UHD Alliance is comprised of 35 companies including television manufacturers such as LG, Panasonic, Samsung, Toshiba, Sony, Sharp, audio companies such as Dolby, and film and television production companies such as Netflix and 20th Century Fox.

The idea then is that if everyone can agree on what features they think UHD should include, then Disney (an example member of the alliance) can produce a movie that Netflix will be able to stream through a Samsung TV, and the eventual image will be exactly what the director at Disney intended.

The result of this alliance was the UHD Premium specification announced at CES 2016. The specification comprises a list of features that should be included in products like TVs and Blu-ray players to ensure maximum compatibility with other content and hardware produced.

Currently, in order to adhere to the UHD Premium specification a product must have:

  • A resolution of at least 3840x2160
  • 10-bit color depth, allowing for 1,024 shades of each of the three primary colors red, green and blue, as opposed to the 256 allowed by the current 8-bit standard.
  • Be capable of displaying pixels at a certain brightness and darkness for HDR purposes (technically this light level is from 0.05 to 1,000 'nits' for LEDs and 0.0005 to 540 'nits' for OLED sets for all you number lovers out there). Adhering to these standards means blacks should look truly dark as opposed to just milky black and whites should really pop.

Samsung and Panasonic are embracing the new standard, with both of their flagship lineups wearing their UHD Premium badges with pride. Sony however have decided to go down a more confusing route and have decided to stick with their internal '4K HDR' label despite their sets all actually meeting the required specification. Philips won't be using the alliance's badge, but its sets don't currently meet the specification anyway.

It's only natural that while a technology is still emerging these problems will continue to exist, but we hope that soon we'll be able to recommend looking for a UHD Premium set without reservation. Until the whole industry unambiguously backs the standard however, we'd still recommend you tread carefully to ensure maximum compatibility.

What is 4K?

UHD Premium: a helpful standard, or just confusing? (Image credit: Panasonic)

What about 8K?

We thought that might come up. You may have heard some of the buzz around 8K resolution – a new visual standard with four times the number of pixels of 4K.

Basically, it doubles the pixel height and width again to yield approximately 32 million pixels. The 8K standard was, until recently, still primarily for the exhibition market (aka movie theaters). To make that many pixels matter, you need to be feeding a pretty big screen and sitting close enough to tell the difference.

We're starting to see commercial 8K televisions come to market, though they'll cost you – and there isn't much in the way of 8K content to truly recommend them. You'll still get the benefit of advanced upscaling from HD or 4K, though, and if you fancy being at the cutting edge of TV technology, an 8K TV is probably what you want.

Confusingly, an 8K display would also be considered 'Ultra HD'.

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. You can find out more in our what is OLED guide.

What is 4K?

Even Honor is getting in on OLED TVs (Image credit: Huawei)

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 4K 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 4K 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.

What is 4K?

Dark (Netflix)

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.

What is 4K?

Want to game in native 4K? You'll need an Xbox One X. (Image credit: Xbox)

What about gaming in 4K?

We had 4K gaming on the PC for a while before consoles, but the more advanced versions of Sony and Microsoft's gaming machines can 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. We'll be sure to get 4K gaming on the next-gen Xbox Series X and PS5, too.

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.

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.

What is 4K?

HDMI 2.0 comes as standard in new 4K TVs (Image credit: iStock)

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.

What is 4K?

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

Should I buy a 4K set now or should I wait?

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.

This year's 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.

  • Check out the very best 4K TVs showcasing the technology

Scott Alexander originally contributed this article.