Updated

What is the Aspect Ratio?
(4:3, 16:9, 21:9)

A TV's (and every other image's) aspect ratio is the proportion between the width and the height of a picture. It is often expressed in the W:H format, where W is the width and H the height. For example, a 16:9 aspect ratio means that for a width of 16 units, the height must be 9 units.

Aspect RatioUsesTVs
4:31.33:1Standard ChannelsOld TVs
16:91.77:1HD ChannelsThe majority of HDTVs
21:92.35:1Most moviesVery few TVs
The most common aspect ratios in the video industry.

Most televisions and computer monitors currently available have an aspect ratio of 16:9, which offers a perfect fit for high definition television shows. However, movies are usually filmed with a ratio of 21:9, which will result in black bars at the top and bottom of the picture when it is displayed on the average TV. To fix this, some manufacturers are producing televisions with a 21:9 aspect ratio. The table above shows the most common aspect ratios.

In theaters, this is why the screen widens at the beginning of a movie. Ads shown before the movie have an aspect ratio of 16:9, while the movie itself is 21:9.

What do the black bars look like on TVs with different aspect ratios?

Black bars on different aspect ratio
Black bars fill the extra space when the aspect ratio of the screen and content do not match.

The position and size of black bars on your television depend on two factors: the aspect ratio of your television and the aspect ratio of the video you are watching. Any mismatch between the two will be filled by the black color. This practice is called letterboxing. The following picture shows the black bars for various televisions and aspect ratios (4:3, 16:9 and 21:9). All televisions have the same diagonal length.

If you do not like having black bars, you have two options available within the settings of your TV: cropping or stretching. Cropping the picture is the equivalent of zooming, but will result in the sides of the picture being removed. Stretching retains all the information, but presents the content in a different proportion.

As you can see, when you watch a 21:9 movie on a normal 16:9 widescreen TV, you will have some black bars at the top and bottom. This is represented by the top center TV in the illustration.

Is a 21:9 TV Worth It?

Comparaison between 21:9 CinemaWide and 16:9 television
A 58" 21:9 TV is equivalent to a 61" for 21:9 media, but only 47" for 16:9 media.

TVs with a 21:9 aspect ratio are rare. A 21:9 TV is only worth it if you almost exclusively watch movies (more than 80% of the time). If you watch normal 16:9 content (like a HDTV channel) on it, you will see black bars on the sides. This reduces the viewing area for 16:9 content considerably. A 58" 21:9 television corresponds to the same viewing area as a 47" TV for 16:9 content, as you can see in the illustration.

Conclusion

The most common aspect ratio for TVs and monitors is currently 16:9, which also corresponds to the aspect ratio of TV shows. However, movies usually have an aspect ratio of 21:9, which will result in black bars above and below the picture if you watch it on your 16:9 screen.

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Questions & Answers

20 ANSWERED QUESTIONS
67
When I download a 1080p movie, the resolution is not 1920x1080 but 1920x800 and there are black bars on my screen. Why?
This is normal. The official resolution of a 1080p Blu-ray is indeed 1920x1080, which corresponds to an aspect ratio of 16:9. However, most movies are shot in 21:9 instead. To fit this on the Blu-ray format, black pixels are used at the top and bottom of the picture. When encoded for the internet, most people strip those black bars, which results in a 1920x800 resolution.
34
What is widescreen aspect ratio? 21:9?
16:9 is generally considered widescreen.
22
How much area are the letterbox bars supposed to cover on a 16:9 TV?
It depends on the aspect ratio of your media. If it is a 21:9 movie, the bars are a few inches tall, as shown in the illustration above.
16
What is 2K?
2K can mean multiple different things. Some people use it as a synonym for 1080p, while others will assign it to a resolution like 2048x1080, or other resolutions that are between 1080p and 4k UHD.
UPDATE: We've updated this answer to make it a broader definition of 2k.
16
Which TVs have aspect ratio auto-switching?
All TVs should be able to do this, but they will handle the process differently from model to model. You might even find the individual ports of some TVs handle aspect ratio auto-switching differently from each other.
14
When talking about aspect ratios, can you explain why we have 1.33:1, for example?
1.33:1 is just 4:3, but normalized (4 divided by 3 equals 1.33).
14
Will the standard aspect ratio change from 16:9 to 21:9? Just like it did from 4:3 to 16:9?
Not in the foreseeable future for TV shows. Most movies are 21:9, though.
9
I'm really considering the Lenovo B750, which has a wide screen (21:9, to be exact). I would maybe watch some Blu-ray DVDs on it from time to time. I really like the idea of more real estate while surfing the web. Guess I am just nervous since some people like it and others dislike it.
We haven't reviewed that monitor (we currently only review TVs). The additional real estate when surfing the web isn't really useful in 21:9, though, because there are no websites designed for this. Therefore, you will most likely browse the web without full screen, which kind of defeats the purpose of the extra width of the screen.
9
On my 32 inch TV, I notice that a 720p/1080p video plays and looks fine meaning that the people, animals etc look proportionate. However on a 23 inch TV, I have noticed that when playing any 720p/1080p videos, the people, animals etc look stretched vertically when covering the full portion of the screen. My question is are there standard sizes like 32 inch, 40 inch, 60 inch etc on which the proportion of the people, animals will look just fine without having to stretch or crop etc? If yes, what will be the best method to know it?
It doesn't depend on the size of the TV, but of its aspect ratio. Assuming you have a 16:9 23", the problem might just be the crop/stretch/zooming option. Look for a setting named 'Picture Size' or something similar and try different values.
7
I have a 65 inch Samsung 1080p 240 Hertz. I buy a lot of Blu ray movies and i would like to watch them without black bars on the top and bottom. how would I go about doing this please help.
Press 'Tools' on the remote, then 'Picture Size' and select 'Zoom'.
5
Does a 4k TV have a 21:9 ratio?
No. A 4k TV has a ratio of 16:9 (3840x2160).
5
If 16:9 ratio has a resolution of 1920x1080, what resolution does a 21:9 ratio have? When I use a monitor with a ratio of 21:9 and a resolution of 2560x1080 (LG 34UM65-P), is the picture ok? With which resolution will the monitor display the movie? 1920x1080 or 2560x1080?
1080p 21:9 movies have a resolution of 1920x800. Your monitor has more pixels than a movie. When you use it to view a movie in full screen, the video is upscaled 1.35 times (both directions), so it will fill all 2560x1080 pixels. This is not an issue, even if there is no 1:1 pixel mapping.
4
I have 65 inch tv in 16:9 full pixel mode the letter box bars are about 4 inches each when playing 21:9 movies, which comes out be approximately 25 % of the screen. In comparison with my old 60 inch it appears the bars are covering a lot more area, is this possible or I am just analyzing too much?
In full pixel mode, this sounds about right. You can always choose a zooming/cropping option if you don't want to bars to show, but you will lose part of the picture.
3
Hello. Do 4K TVs eliminate the problem with aspect ratios? Will any movie I watch be displayed in an aspect ratio of 21:9?
No. Aspect ratio is a description of the screen's proportions, and is independent of the screen's resolution. A 4k TV with an aspect ratio of 16:9 can still only display a 21:9 signal with black bars on the top and bottom of the screen.
3
The answer is not entirely wrong, but incomplete: 2k is a bit of a broad term. 2k can also stand for 2048x1080, and a few other resolutions with anything between 1920 and 2048 as the horizontal pixel value. Vertical pixel values can also vary. They are not restrained to just 1080! Example: 2048x858 for CinemaScope-cropped DCI 2K.
The definition being so broad means that watching a 2k movie in a common projection resolution on a "2k" monitor can lead to resizing and letterboxing.
Good point. We'll update the answer to make it clear that there are multiple meanings. Thanks! UPDATE: Corrected one of the incorrect resolution suggestions.
2
This question is for games. Will a monitor that is 21:9, 3440x1440, actually show more on the sides than a 4k 16:9 monitor?
As long as your source device can output that resolution and the game also supports that resolution then yes, it would.
2
Why don't TV manufacturers make their televisions 21:9 capable instead of 16:9? Is it a cost/money thing?
TVs are still geared more toward watching TV shows and playing video games (16:9) than they are to watching movies (21:9), so it's less about cost and more about the manufacturers tailoring to what most people want.
2
The screen I show my Windows Live Movie Maker on is 22" wide and 14" high. Should I use 16:9 or 4:3 aspect ratio?
4:3 will fill up a little bit more of the screen, so use that.
1
Is there any way to change the aspect ratio of a Sharp XR-llXC projector from 4:3 to 16:9?
Your projector native aspect ratio is 4:3 and that can't be changed. By default, it will display 16:9 content with black bars on top and bottom of the screen. The 'image shift' function of your projector can remove one of the black bar but not both. You could also see if there is special anamorphic lenses available for your projector. Those lenses, with the help of a software, could convert 4:3 to 16:9 but with some degradation in the picture quality.
1
4K is not a 16:9 ratio. 4K is not 3840x2160. 4K is 4096x2160. 4K is 17:9. 3840x2160 is UHD (UltraHD) 16:9.
You are technically correct. But now, '4k' is a broad term which refers to a resolution of about 4000 horizontal pixels. When talking about TVs, this is a resolution of 3840x2160 and you will see it in all the brands advertising (Samsung, LG, Sony) where they include one or both terms (4k and UltraHD). The standard for films is different.
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