When you're shopping for a TV, one of the most obvious and prevalent numbers is the resolution.
But what does 4K mean? Is that more than Ultra HD? Is Blu-ray 1K? If 4K is four times greater than 1080p, does that mean 4K is 4320p?
Well, in order: depends, sometimes, no, and no.
Resolution, in the sense I'm talking about here, refers to the number of pixels that compose the picture on the TV. A single pixel, or discrete picture element, consists of a tiny dot on the screen. On today's TVs there are between roughly one million (for 720p TVs) to eight million (for 4K Ultra HD TVs) such dots. You'll have to look very closely, or whip out a magnifying glass, to discern one.
Although it's the most common specification used to sell TVs these days, partly because "eight million pixels" sounds really impressive, resolution is not the most important ingredient in picture quality. Just because a TV says "4K Ultra HD" doesn't always mean it's better than a 1080p TV. It usually does, but not always, and for reasons that have little to do with resolution. See my article Why 4K TVs aren't stupid (anymore) for more on that.
That said, it's still worth understanding the various resolutions used by TV makers and others. Here a bit more, ahem, detail.
4K or Ultra HD
Let's start at the top of the current TV market: 4K. This is a good place to begin, as it lets us talk about the basis for the vast majority of the confusion when it comes to resolution.
The short version is this: When it comes to TVs, 4K and Ultra HD (or UHD) are referring to the same resolution. Those TVs, along with Ultra HD Blu-ray, and nearly all UHD streaming content from Netflix, Amazon and others, is 3,840x2,160 resolution.
Here's the long version:
Select large-screen resolutions
|Resolution name||Horizontal x Vertical pixels||Other names||Devices|
|UHD||3,840x2,160||4K, Ultra HD, Ultra-High Definition||TVs|
|WUXGA||1,920x1,200||Widescreen Ultra Extended Graphics Array||Monitors, projectors|
|1080p||1,920x1,080||Full HD, FHD, HD, High Definition||TVs, monitors|
|720p||1,280x720||HD, High Definition||TVs|
The problem is that 4K means something different whether you're talking about a TV in your home, or a projector in a theater.
Technically, "4K" means a horizontal resolution of 4,096 pixels. This is the resolution set forth by the Digital Cinema Initiatives. Because movies vary in aspect ratio, which refers to the exact shape of the rectangle of screen, no vertical resolution is specified.
So yes, the pedants are correct. Ultra HD TVs aren't technically "4K" since their resolution is 3,840x2,160. However, it doesn't matter. 4K is way easier to say than 2,160p or Ultra HD, and when anyone runs a survey asking about it, the vast majority of you (and us, FWIW), greatly prefer "4K." So does Google. Amazon just uses both.
Since the pixel difference is 13 percent and it's nearly impossible to see even larger differences, we'll file this under "why does anyone care" (but people really care, as I'm sure we'll see in the comments).
8K follows the same logic. If you're talking about TVs, it's twice the horizontal and vertical of 4K TVs: 7,680x4,320. This isn't a cinema resolution yet, at least not outside of the experimental stage. We're a long way away from 8K TVs being anything close to mainstream.
Before "4K" became common, you'd almost never see "2K." It was pretty much just a cinema resolution, which is why you'll sometimes see used to refer to a "master format." Most digital cinema projectors used in theaters are 2K resolution (some are less). It's 2,048 pixels wide, and again, no vertical resolution is specified by the DCI.
But now that "4K" has gained traction as a term used to describe TVs and content, "2K" is becoming increasingly common as shorthand for the 1080p resolution used by most HDTVs, as well as Blu-ray. It's not technically accurate, but that didn't stop "4K" from becoming more popular than UHD.
1080p or Full HD
Remember how we talked about digital cinema resolutions only specifying the horizontal resolution?
Well, TVs, on the other hand, have historically used the vertical to describe resolution (going back to the glass tube days). So 1080p is the vertical resolution. Nearly all HDTVs have an aspect ratio of 1.78:1 (16x9, aka "widescreen"), so that means a horizontal resolution of 1,920 pixels (1,920x1,080).
This is another source of confusion, since decades of TV discussions have talked about vertical resolutions, and then all of a sudden we're talking about "4K TVs," which refers to the horizontal resolution. Don't blame me, it wasn't my idea.
That means 1080p is not "1K." It's 2K, as much as UHD TVs are 4K. Which is to say, at 1,920x1,080 they're close to the DCI's 2K specification of 2,048. That said, most people don't call 1080p 2K; they call it 1080p or Full HD.
By the way, 1080i is the same resolution as 1080p, but only these days appears as a source resolution, not as a TV resolution. There are no 1080i TVs anymore, but many HDTV broadcasts are still in 1080i.
Roughly half the number of pixels of 1080p. Only the smallest and cheapest TVs are 720p anymore. However, all ABC, Fox, ESPN, and their affiliated/sister channels broadcast at 720p. This goes back to the initial HD transition at the turn of the century. And if you're wondering why your TV doesn't say "720p" on those channels, check this out.
Monitor resolutions: WUXGA, WXGA, WXXXGA, WXCBGBSA, WXLADYGAGA
In the computer world they use an incomprehensible and shockingly un-user-friendly jumble of letters to describe resolution. Well, not "shockingly" since these are computers.
Look, I'm a computer guy, building my own PCs since the early 90s, and even I can't tell you what half these letters mean. I can understand that initially they were implemented to make things easier, but we've got so many resolutions and combinations that now they're just annoying.
Basically, the ones you're most likely to see are FHD (1,920x1,080) and WUXGA (1,920x1,200). The rest, you can dive into and print yourself a cheat sheet from this.
Fortunately, the only time most of you will come across this letter goulash is if you're looking for a cheap data projector or a computer monitor.
When you boil it all down, here's the takeaway: Your current TV (unless it's really new) is HD, either 720p or, more likely, 1080p. New 4K Ultra HD TVs have four times as many pixels as 1080p.
Here's where we remind you that more pixels doesn't necessarily mean a better picture. There are other aspects of picture quality, such as contrast and color, that are far more important than resolution. That said, if you're buying a new midrange or high-end TV, it will probably be UHD anyway.
Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED vs. Plasma, why 4K TVs aren't worth it and more. Still have a question? Send him an email! He won't tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter@TechWriterGeoff or Google+ and check out his travel photography on Instagram.