What's the difference between HD, Full HD, 2K, 4K and 5K? Display resolutions explained

With countless smart devices available on the market, all with different sized displays, varying screen resolutions and special names for these technologies, it’s not easy to know the difference between them all. FHD this and WQHD that, what the hell do any of them mean?

Well, the most important thing to note is the more pixels on the screen, the higher the definition of images and videos will be and the better things should look. But when frequently-used display resolutions are referenced with complicated names such as qHD, WQHD and what not, it’s difficult to know what is what.

We’ve laid out what these complex-sounding screen terminologies mean in the simplest terms so that the next time you buy a device, you’ll know exactly what you’re getting. First off, let’s start with the basics.

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Never has a technical specification been overused and misused as much as High Definition or HD. The term has become synonymous with anything that raises the detail or quality over-and-above something that came before. When we're talking about display resolutions though, the term HD is based on the original resolutions of HD TV.

When HD TV first came along there were a handful of broadcast resolutions and display resolutions used. The most basic was 1,280 pixels wide by 720 pixels tall, shortened to 720p. The lower-case p refers to “progressive scan” as opposed to say 1080i, which is 'interlaced' but we won't get bogged with those here.

These days when we say HD we're talking about what gets called 'Full HD', a resolution which measures 1,920 x 1,080 pixels, often called 1080p. This display resolution is common on Smart TVs and many modern smartphones, PCs, laptops and monitors. Both HD resolutions here use a 16:9 aspect ratio (so there are 16 pixels horizontally for each 9 vertically), which can be described as widescreen. However, on a phone 1,280 x 720 becomes 720 x 1,280 when it's held normally.

The other thing to remember is that no matter the screen size of say a Full HD display, whether it’s a 4in smartphone or a 65in TV, the number of pixels remains the same but just change in size, so depending on whether they are smaller or larger, they will look softer or sharper. For instance, a Full HD smartphone has far more detail (sharpness), usually described as pixels-per-inch (ppi) than a Full HD monitor because the smaller screen is a higher density but has the same number of pixels, so a sharper picture.

In the smartphone revolution of the last five or so years, manufacturers have been desperate to put higher resolution screens into phones even where they are not needed. It's often argued that resolutions above that of Full HD are wasted on such comparatively small panels as even people with perfect vision find it hard to spot any difference. Nevertheless, phone makers have done it anyway, probably for marketing purposes. As a result, Quad High Definition (QHD) screens have become a popular choice in modern handsets.

QHD is four times the definition of standard 720p HD, meaning you can fit the same number of pixels as four HD displays into a QHD display of the same size, namely 2,560 x 1,440 pixels, or 1440p. As with all HD-derived resolutions, this one has a wide 16:9 aspect ratio, so QHD can also be referred to as WQHD (Wide Quad High Definition), it’s the same thing, but some manufacturers put a W in front of the QHD to show that it has the wide aspect ratio.

^The above AOC AG322QCX gaming monitor natively runs at 2,560 x 1,440

Sometimes QHD or WQHD is referred to as 2K, with the idea that it's half the 4K HD resolution found on high-end TV sets (more about that later). But most of the time the 2K name is derived from the larger of the pixel measurements being over 2,000 pixels. Technically, the resolution standard for 2K is 2,048 × 1,080, meaning QHD is actually much better in resolution. QHD could even be referred to as 2.5K, but some people resist in calling these displays 2K.

qHD is not to be confused with QHD. Despite having a very similar name, qHD stands for Quarter High Definition and is a display resolution of 960 x 540 pixels - one-quarter of 1080p Full HD.

This is used much less frequently these days. It was often found on high-end smartphones and handheld consoles -- such as the Playstation Vita -- around 2011, and if used today is usually found on much smaller device displays for a relatively high pixel density when anything higher would be wasteful.

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4K and Ultra High Definition (UHD) resolutions can be a cause for confusion because both terms are often used interchangeably when actually they are not the same. So we’ll need to do a little explaining of these, too.

True 4K displays are used in professional production and digital cinemas and feature 4,096 x 2,160 pixels. UHD is different because it is a consumer display and broadcast standard with a resolution four times that of a Full 1080p HD resolution: 3,840 x 2,160 pixels. The difference comes down slightly different aspect ratios between digital cinema and home displays. UHD is another 16:9 aspect ratio standard, which means screens are backwards compatible with Full HD content.

^ Marketing types are using 4K and Ultra HD interchangeably, but there are small differences

Both 4K and UHD definitions could be shortened to 2,160p, to match HD standards that have preceded them, but this would make things even more confusing because while the pixel difference is relatively marginal, they are still different. Some brands prefer to stick to just UHD moniker when marketing their latest TV to avoid confusion, but for the ease of marketing, it has meant that the two terms continue to be used interchangeably.

So far, most phone manufacturers have avoided putting ridiculously high-resolution 4K screens into phones in a bid to preserve battery life. Apart from Sony's previous endeavours, that is.

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5K is still somewhat of a niche, as not many manufacturers produce 5K panels. Suffice to say, they exist; from Apple's 5K iMac to Iiyama's ProLite XB2779QQS, which run at a ridiculous resolution of 5,120 x 2,880. That's double the resolution of a QHD panel, which to the naked eye will still look razor sharp. 5K monitors are just in a league of their own. Of course with all those pixels, you'll need a multitude of graphics cards to consistently output over 60Hz.

There's also 8K, the next resolution fad that many TV manufacturers are bragging about. There have been a few iterations by panel manufacturers, such as Dell with its UP3218K, which runs at a staggering resolution of 7,680 x 4,320. These haven't quite hit the mainstream market, as there's not enough content nor graphics power that can handle 8K at an agreeable refresh rate. Still, it's worth keeping your eyes peeled on 8K monitors.