Why 16:9 aspect ratio was chosen for HD?

With High Definition (HD) content becoming mainstream, the aspect ratio of 16:9 has gained lot of prominence especially in the last few years due to the popularity of LCD/LED TVs and even a stubborn company like Apple Inc which is notorious for usually being “against mainstream” acknowledged the standard when it switched to the mainstream widescreen 16:9 ratio for the iPhone 5.


But what is so special about widescreen 16:9? Why not 25:16 or 20:7 anything else? Lets look into the history of video industry to find out why.

Even till just a few years ago, the popular standard was 4:3 (1.33:1). Most of us would be able to recollect nostalgic memories of our box-shaped CRT Television sets which in fact had this 4:3 ratio.


But why was it 4:3 and not 5:4 or 6:5? To know why, we have to rewind back to 1892 when Thomas Edison invented film and had to determine the image ratio for his film. Since the sprocket perforation of his lab equipment had a ratio of 4:3, he finalized it as the ratio for the full frame as well.


Over the next few years, the standards committee also conducted several experiments and found that the human eye’s field of view was of the ratio 4:3 (155° H x 120° V) and hence it was continued as the standard for film, camera and later for TV as well.

When TVs became mainstream by 1960s due to aggressive marketing by companies like Sony, Panasonic and Motorola (yes, Motorola was one of the pioneers in Television industry back then) and almost every home in US could afford a TV, the entertainment industry began to witness a dramatic shift in the viewing habits of consumers. People preferred to watch TV at home rather than going to a theater and this set alarm bells ringing in the Hollywood industry which had to come up with something new to bring back people to theaters.


Hollywood industry had to be something different compared to the home television. As a result, Hollywood came up with widescreen movies with more picture content (especially in landscape shooting) which created “WoW” factor and was successful in drawing back crowds to theaters. Since there was no standards body, several aspect ratios started cropping up across different film houses, some of the popular ones being Panavision ratio of 2.20:1 and a much wider format called CinemaScope of ratio 2.39:1.



This way, Hollywood managed to get back its audience for movies, while casual viewing at home like soap operas & news continued with the 4:3 ratio. For a long time, the TV remained with 4:3 ratio and had 525 horizontal lines (Vertical resolution), but technology was improving at a rapid pace.


When the technology was ready for Plasma & LCD screens with much higher resolutions, the International standards body took up the task of coming up with a new format called HD (High Definition) with a minimum of 720 pixel as vertical resolution (1080p for full HD). The standards body wanted to use this opportunity to come up with unified standard for aspect ratio which would accommodate all the popular existing aspect ratios so that the industry could channelize all their efforts into one format. There was no problem in displaying videos of any formats but doing so would lead to lot of wastage of space. For example, a widescreen video could be played on a normal TV of 4:3 aspect ratio but doing so would lead to huge black borders on top and bottom of the screen which is also called letterboxing like this:

Similarly, a 4:3 video content could be played on a widescreen TV but that would lead to black borders on the sides of the TV (pillarboxing) like this:


The standards committee now had a challenging task of coming up with a compromise which would minimize the wastage of screen-space. i.e They had to finalize on an aspect ratio which would be most optimized for all the popular standards. The most popular standards which they considered were the 1.33:1(i.e 4:3) which was used in film camera & home TV, the 2.20:1 & 2.39:1 used by Hollywood.

What the committee did next was very interesting. A member of the committee (Dr. Kerns Powers) created cardboard cut-outs of all the popular aspect ratios of equal area and started placing them one over the other with overlapping centres.


It was found that the outermost (largest) rectangle which accommodated all the smaller rectangles efficiently had the same aspect ratio of the innermost rectangle and this ratio was 1.78 which when rounded off to whole numbers was 16:9. In mathematical terms, it means that the geometric ratio of the extreme ratios (1.33 & 2.39) was approx 1.78 i.e 16:9.


Hence, for HD, 16:9 was finalized as a compromise which could display all of the popular aspect ratio formats most efficiently by minimizing black borders and it has remained the most popular & widely used aspect ratio till date.

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