The aspect ratio of an image is the proportional relationship of the width to the height. You will recognize it as two numbers separated by a colon in an x:y format. For instance, a 6 x 4 inch image has an aspect ratio of 3:2. An aspect ratio does not have units attached – instead, it represents how large the width is in comparison to the height.
This means that an image measured in centimeters will have the same aspect ratio even if it was measured in inches. The relationship between its width and height determines the ratio and shape, but not the image’s actual size.
However, an image’s aspect ratio will change depending on the medium in which it is presented. The aspect ratio of an image displayed on a computer will be different from the aspect ratio of that same image displayed on a phone.
Aspect ratios are a critical part of web content because images need to be uploaded at different aspect ratios for different uses, like desktop vs. mobile or blog vs. social media. When you use the right aspect ratios it ensures your images are displayed as intended without stretching or resolution loss.
A 1:1 ratio means that an image’s width and height are equal, creating a square. Some common 1:1 ratios are an 8 x 8 inch photo, a 1080 x 1080 pixel image, or typically any profile picture template on social media sites (think Facebook). This aspect ratio is commonly used for print photographs, mobile screens, and social media platforms, but it’s not ideal for most TV or digital formats.
The 3:2 ratio has roots in 35 millimeter film and photography and is still widely used for print sizes. Images framed at 1080 x 720 pixels or 6 x 4 inches are set within this aspect ratio.
A 4:3 ratio is typically used for TV displays, computer monitors, and digital cameras. For every 4 units of width, there are 3 units of height, creating a rectangular shape. An image sized at 1024 x 768 pixels or 8 x 6 inches fits a typical 4:3 ratio.
The 16:9 ratio is mostly seen on presentation slides, computer monitors, or widescreen TVs. This international standard recently replaced the 4:3 ratio for monitors and TV screens, creating a slimmer, more elongated rectangular shape compared to the 4:3 format. Common resolutions in the 16:9 ratio are 1920 x 1080 pixels and 1280 x 720 pixels.
How to Measure Image Size
Unlike aspect ratios, image size determines an image’s actual width and height in pixels. Image size is the dimensions of an image. You can measure image dimensions in any units, but you’ll typically see pixels used for web or digital images and inches used for print images.