The standard size for high definition widescreen televisions and most computer monitors, 16:9 is the most common aspect ratio used today. It is generally associated with video shot for TV and the Internet since film aspect ratios are typically wider in order to achieve a more cinematic look.

Why is widescreen 16x9?

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.

How do I choose aspect ratio?

Aspect ratio is primarily dictated by the size of your camera's sensor, taken from the width and height of an image (W:H). For instance, if your camera sensor is 36mm wide and 24mm high, its aspect ratio would be 3:2 (not 36mm x 24mm).