What is Aspect Ratio?
Definition
Aspect ratio is the proportional relationship between a video frame's width and height, written as W:H (for example 16:9). It describes the frame's shape, not its size, and is independent of resolution.
Aspect ratio is expressed as two numbers separated by a colon, like 16:9 or 9:16, showing how width relates to height. It defines the shape of the frame regardless of how many pixels it contains. A 1920x1080 video and a 1280x720 video are both 16:9 because they share the same proportions, even though their resolutions differ.
Different platforms expect different ratios. 16:9 is the widescreen standard for YouTube and TV, 9:16 is vertical for TikTok, Reels and Stories, 1:1 is square for some social feeds, and 4:3 is the older standard from analog TV. Choosing the right ratio lets your video fill the screen on its target platform.
Changing aspect ratio always involves a trade-off. To fit content into a new shape you either crop it (cut off parts of the frame) or pad it with bars: letterboxing adds bars on the top and bottom, while pillarboxing adds them on the left and right. People often confuse aspect ratio with resolution, but resolution counts pixels while aspect ratio describes only the frame's proportions.
Quick facts
- Written as width:height, e.g. 16:9, 9:16, 1:1, 4:3
- 16:9 is widescreen (YouTube, TV); 9:16 is vertical (TikTok, Reels, Stories)
- Describes frame shape only, and is independent of resolution
- Changing it requires cropping or adding bars (letterboxing/pillarboxing)
- 1:1 is square; 4:3 is the older analog TV standard