An aspect ratio is a ratio of the width and height of an object, most commonly an image. An image that is, for example, 6 inches wide and 4 inches tall has an aspect ratio of 6:4 — or 1.5:1 (6 / 4 = 1.5).
A common aspect ratio for a widescreen format might be 16:9, where an older, more square TV format would have been closer to 4:3.
Where aspect ratio is simply a ratio, it is typically unitless. For example, an image 160 pixels wide by 90 pixels tall has the same aspect ratio as an image 16,000 meters wide and 9,000 meters tall.
