Why is 3840x2160 considered 4k?

[MahmoudAyoubi]

Today we consider 1920x1080 1080p, and 1280x720 is considered 720p so they are both labelled by their width but with 4k 3840x2160 is only 2x more than 1080p so it is really 2k. but why do brands call it 4k and make tvs and projectors and cameras so overpriced almost 10x more expensive than a 1080p when they are only doubling the pixels?

 

[Novuake]

Doubling?

Literally do the math.

1920x1080 = 2.7million pixels. So yes, 2K.

3840*2160 = almost 8.3millions pixels.

So yeah, not just double.

 

[MauveCloud]

They call it 4k because 3840 rounded to the nearest thousand becomes 4000 (I guess it sounds more impressive to go by the horizontal resolution than by the vertical resolution). Also, like Novuake pointed out, it's double the pixels in each direction which comes out to quadruple the total pixels. Yes, the price is still more than quadruple, but I think that's because 4k tvs and monitors are still a bit of a niche market, and the production runs have been small. There could also be issues with the yield, the chips for signal processing have to be more powerful, and there are probably additional reasons for the extra expense.

 

[Traciatim]

Because marketing.

 

[BowserJr395]

The numbers like 1080p and 720p are respective of the resolution's height - e.g. 1920x1080 is 1080p, 1280x720 is 720p, and so on. The 'K' numbers such as 2.5K and 4K are respective of the resolution's width - for example, 2560x1440 is called 1440p due to it's height of 1440 pixels, but it is also referred to as 2.5K, due to it's width being rounded to about 2,500 pixels. 4K is 3840x2160, and it's width is 3840 pixels. This can be rounded to about 4,000 pixels, hence the notation of '4K'.