We've been hearing a lot about 4K lately: the Roku 4 will have it, the Apple TV won't, etc. That's all very interesting, but what exactly is 4K? Sure, it's a fancy new kind of high-definition standard, but how much better is it? And why is called 4K, anyway? Here's everything you need to know about the new wave in HD television.

What Is 4K?

You probably already know that 4K means a special kind of high definition. But what exactly is it, and why do we call it “4K?”

Well, the “4K” name has its roots in older HD terminology. When we first started having the option to enjoy video in “high definition,” people outside the industry mostly just called it “HD” (heck, a lot of us still do). But as high definition technology improved, we were soon able to choose formats with an even higher definition. That's when you started seeing TVs and videos labeled with “720p” and 1080p”

What these names refer to is the number of pixels (you know pixels – they're the tiny little glowing dots that make up your TV screen). A 720p TV has 720 rows of pixels – that is, it's 720 pixels high. It's a simple way to measure how crisp the resolution would be (if we used the total number of pixels instead of the number of pixels on the shortest side, we've be calling 1080p TVs “2,073,600p TVs” – not quite as catchy). 1080p is better than 720p because it has more pixels. Easy.

Okay, so what is 4K? Well, it's the short way to write 4,000. So a 4K TV must have 4,000 pixels on its short side, right?

Unfortunately, it's not quite that simple. The 4K standard that most manufacturers use is the DCI 4K standard, which mandates a 4096 x 2160 resolution. Under the old naming conventions, that would be “2160p.” But some bright person must have realized that 4,000 sounds more impressive than 2,160, so the naming convention was changed. 4K (4,000) still refers to the number of pixels along one side of the screen, but it now refers to the pixels on the long side, not the short side.

That's a long way of saying that 4K is a confusing name for a 4096 x 2160 resolution, which has twice as many pixels along the short edge as the old 1080p HD does (some 4K TVs have fewer pixels along the long side, but we'll get to that in a moment).

Let's borrow a picture from Wikipedia and show that difference visually:

4k comparison

The more pixels, of course, the crisper the image – especially if you imagine all of these screens to be the same size. DCI 4K has more than four times the number of pixels that 1080p does!

UHD vs. DCI 4K

Okay, you may have noticed that the image in the last section included something called “UHD.” So what was that?

Well, UHD (or “ultra-high-definition”) is one of the two major 4K standards, though some die-hards don't consider it to be “true” 4K at all.

The UHD standard, like the DCI one, has 2160 pixels on the short edge. The difference is that UHD 4K uses a 16:9 aspect ratio instead of the 256:135 one that DCI uses. To put it more simply, the UHD version doesn't have as wide of a screen. As a result, the UHD 4K actually doesn't quite have 4,000 pixels along its long side – it only has 3,840.

The film industry prefers the DCI aspect ratio, so movies will fit more nicely into screens that use the DCI standard. When shopping for a 4K TV, be careful: some manufacturers label their TVs simply as “4K,” not mentioning that they use the UHD standard instead of the DCI one. Make sure you're looking at a the type of 4K TV you want before you buy anything. Right now, it's a bit easier to find UHD TVs than it is to find DCI ones.

The Present and the Future

So there you have it: 4K is a fancy name that just means 2160p, and DCI's 4096 x 2160 resolution is the gold standard. But what does 4K mean for your viewing experience?

Obviously, 4K video looks nicer than videos shot in older HD standards. But it will be a while before the industry catches up. Some new streaming boxes (like the Roku 4 and the Fire TV) are 4K equipped, but content providers aren't quite as into it yet. For instance, HBO's new Roku app doesn't take advantage of the latest Roku's 4K abilities. Also, the new Apple TV isn't 4K capable at all. This reflects the industry's belief that most consumers aren't yet invested in 4K. Most of us don't have a 4K TV, and most of us don't have fast enough internet to stream 4K video.

That said, 4K is the wave of the future. It may just be for early adopters now, but it won't be long until 4K is standard in the streaming industry. It's an exciting time to be a streamer.