aspectratio

Aspect ratio is the proportional relationship between the width and height of an object such as an image, photograph, video frame, or display screen. It is typically expressed as a pair of integers separated by a colon (for example, 16:9), representing the relative widths and heights, and it is a dimensionless quantity that guides how content is framed and displayed.

In practice, aspect ratios affect how scenes are composed and how they appear on different viewing devices. Common ratios include 4:3 (classic television and computer monitors prior to widescreen), 16:9 (standard HDTV and most modern video), and 21:9 (ultra-wide formats used in some cinematic and gaming contexts). In still photography, 3:2 and 4:3 are common. Cinema often uses ratios such as 1.85:1 or 2.39:1. Some displays use native aspect ratios that differ from a video’s content, leading to letterboxing (black bars above and below) or pillarboxing (bars on the sides) to preserve the original framing.

Pixel aspect ratio and display aspect ratio are related concepts. If pixels are square, the display aspect ratio matches the content’s aspect ratio; if not, the pixel aspect ratio can cause distortion unless corrected. When resizing or scaling video, maintaining the intended aspect ratio avoids stretching; this may require cropping or adding bars.

Formulas: given a width W and an aspect ratio a:b, height H = W × b ÷ a. Conversely, given height H, width W = H × a ÷ b. Understanding aspect ratio helps in design, photography, film, and video production.