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

4K Ultra HD (ultra high definition) is the resolution that brings you more pixels than ever to your home TV.

Not long ago, Full HD (full high definition) was the sharpest picture you could get. This brings four times as many pixels as HD. But now, enter 4K resolution, which has completely changed the level of visual detail and clarity we’ve come to expect from our screens.

Whereas traditional HD is limited to 1920 vertical columns and 1080 horizontal rows of pixels, Ultra HD has a total resolution of 3,840 pixels by 2,160 – a slightly smaller resolution than the 4,096 x 2,160 pixels seen on most cinema screens (that, for the record, is called Cinema 4K).

It’s pretty hard these days to get a TV that isn’t 4K, with even budget small TVs opting for the detailed resolution to entice viewers. And some of the truly premium sets out there are now opting for 8K resolution instead – but 4K is still the king for now, and near enough all the new sets announced at this year’s CES 2020 expo are pushing the Ultra HD resolution.

At the end of the day, though, it might not be the raw resolution of 4K that tempts you into your next TV purchase, but the inclusion of other cool technologies like High Dynamic Range (HDR), Quantum Dot and OLED panels.

But before we get into the specifics of each technology, here’s a video outlining 4K in a nutshell.

What is 4K?

Put simply, 4K means a clearer picture. To achieve this, it’s more pixels (8,294,400 to be exact) on the screen at once being used to create images that are crisper and capable of showing more details than standard HD. That’s it.

What is the resolution of 4K?

4K resolution, at least the way most TVs define it, is 3840 x 2160 or 2160p. To put that in perspective, a full HD 1080p image is only a 1920×1080 resolution. 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.

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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.

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.

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 3840×2160
• 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.

And 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. It’s a regular pixel party – though you can find out more about the new resolution in our 8K TV guide.

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

Should I just get an 8K TV instead?

If you want? 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.

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 years after they first came to market – and it’s generally accepted that they don’t have the longevity of LCD screens.

I’ve heard Netflix has been streaming in something called HDR. What is that?

HDR, UHD, OLED… there’s no shortage of acronyms in home entertainment.

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 Instant 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.

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. And 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.

So what can I watch in 4K?

Your best UHD options right now come from Netflix and Amazon.

Netflix is leading the 4K streaming waters with most of its original shows (The Defenders, House of Cards, Dark, The Blacklist) being available in 4K, alongside select films (Ghostbusters, The Smurfs 2). 

The selection might be more limited than the amount of HD content, but it’s increasing day by day. 

Amazon has also 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.

Both streaming services say even more content is on its way and expects the roll-out to ramp up once more TV watchers make the jump to the higher-resolution standard.

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.

Some recent big video games available in 4K on various platforms include Red Dead Redemption 2, Spiderman 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.

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 3820×2160-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.

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

If you’re buying a TV that’s 50-inches and above you should absolutely think about investing in 4K. All of the major players are embracing it as the new standard, and the amount of content is only going to increase over time. 

If you’re buying a TV smaller than 50-inches, the answer is less obvious.

The problem is not that 4K doesn’t make enough of a difference at these sizes, but instead that the additional technologies that have been combined with 4K in most sets haven’t trickled down to the smaller models just yet. 

As a result, while it’s totally possible to get a 4K TV that’s as small as just 40-inches, at this point it’s unlikely to have a decent level of HDR (which we’d consider as going as bright as 1000 nits or more), 10-bit color, or wide color gamut. 

Sure you’ll get the right amount of pixels, but they won’t have the additional technologies to make them look really beautiful. 

Eventually they’ll make their way to small TVs, but for now 4K is at its best at 50 inches and above, where you can get all the bells and whistles that really matter. 

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Scott Alexander originally contributed this article.