Home : Technical Terms : Aspect Ratio Definition

Aspect Ratio

An aspect ratio describes the relationship of an object's width to its height. It is commonly used in computing to describe the proportions of a rectangular screen.

Aspect ratios are written as mathematical expressions, using the following format:

width:height

For instance, a monitor that is 20 inches wide by 15 inches tall has an aspect ratio of 20:15. After reducing the fraction (dividing each number by the lowest common denominator – in this case 5), the aspect ratio is 4:3, or "four by three." 4:3 was the aspect ratio used by standard definition (SD) televisions, before HDTV.

A square screen or image has an aspect ratio of 1:1. A screen that is twice as tall as it is wide has an aspect ratio of 1:2. If a screen 50% wider than it is tall, its aspect ratio is 3:2. Both HDTVs and 4K televisions have aspect ratios of 16:9 ("sixteen by nine"), meaning they are almost twice as wide as they are tall. An HDTV, for example, has a resolution of 1920x1080 pixels. The 16:9 aspect ratio of HD resolution can be verified using the math below.

1920 ÷ 16 = 120. 120 x 9 = 1080.

Alternatively, 1920 ÷ 120 = 16. 1080 ÷ 120 = 9.

4K is simply twice the width and height of HD, or 3840x 2160. Therefore, 3840 ÷ 240 = 16. 2160 ÷ 240 = 9.

While most modern televisions have 16:9 aspect ratios, other types of screens may be longer or taller. For example, many tablets and computer monitors have 16x10 (or 8x5) aspect ratios, which means they are slightly taller relative to a standard HD display. Smartphones often have extra long screens when held sideways (a.k.a. landscape view). For example, the Samsung Galaxy S8 has an aspect ratio of 18.5:9 and the iPhone X has an aspect ratio of 19.5:9. When watching HD video on these devices, the video does not fit the full width of the screen. Instead, black bars are displayed on the sides because the aspect ratio of the video is not as wide as the aspect ratio of the screen.

NOTE: HD (16:9) is 25% wider than SD (4:3 or 12:9). That is why modern flatscreen displays appear wider than older CRT televisions.

Updated: December 2, 2017

Cite this definition:

https://techterms.com/definition/aspect_ratio

TechTerms - The Tech Terms Computer Dictionary

This page contains a technical definiton of Aspect Ratio. It explains in computing terminology what Aspect Ratio means and is one of many technical terms in the TechTerms dictionary.

All definitions on the TechTerms website are written to be technically accurate but also easy to understand. If you find this Aspect Ratio definition to be helpful, you can reference it using the citation links above. If you think a term should be updated or added to the TechTerms dictionary, please email TechTerms!