Image Dimension & Aspect Ratio Calculator

An aspect ratio calculator shows the proportional relationship between the width and height of an image, video, or screen, such as 16:9 or 4:3, and helps you resize while keeping those proportions. Distorted or unexpectedly cropped images are a common problem when assets are scaled by eye, especially across responsive layouts, social platforms, and video players. This tool solves that by simplifying any pair of dimensions to their lowest ratio and calculating the missing dimension when you enter a new width or height.

Enter the original width and height in pixels to see the simplified ratio and the decimal ratio. To resize, add either a new width or a new height and the tool calculates the matching dimension so the proportions stay the same. Use the result when exporting from a design tool, setting width and height attributes in HTML, defining the aspect-ratio property in CSS, or preparing images for a platform that requires a specific ratio. Round to whole pixels and check that the final dimensions meet the platform limits.

Correct proportions keep images looking professional and prevent layout shifts that frustrate visitors and can affect page experience metrics. Setting explicit dimensions or an aspect-ratio value lets the browser reserve space before an image loads, which improves perceived performance. The calculation happens in your browser without any upload. Clear, formula-based answers to questions such as how to calculate an aspect ratio are the kind of concise content search engines and AI assistants can accurately present.