Find the shape of an image or screen (its "aspect ratio", like 16:9) and resize it without stretching. Enter a width and height to get the ratio, or enter a ratio plus one new dimension to get the other. Everything runs in your browser.
About this aspect ratio calculator
An aspect ratio is the shape of a rectangle expressed as width to height — for example 16:9 (widescreen video and most monitors), 4:3 (older screens) or 1:1 (a square social post). It describes the proportions no matter the actual pixel size. This free calculator does two jobs. The find the ratio section takes any width and height and reduces them to their simplest ratio, plus a decimal version. The resize section helps you scale an image or video without distorting it: give it the ratio and one new dimension, and it works out the other so everything stays in proportion. It is handy for photographers, video editors, designers and anyone fitting content to a screen. All the maths runs in your browser.
Frequently asked questions
- What is an aspect ratio?
- The shape of a rectangle written as width:height, like 16:9 — the proportions, regardless of pixel size.
- How do I resize without stretching?
- Keep the same ratio: enter the ratio and one new dimension, and the tool gives the matching other side.
- What is 16:9?
- The widescreen ratio used by most TVs, monitors and online video — e.g. 1920 × 1080 pixels.
Understanding Aspect Ratio Mathematics
An aspect ratio is a mathematical relationship between the width and height of a rectangle, expressed as a ratio of two numbers. This convention originates from the need to maintain consistent proportions when scaling images or displays across different pixel densities. Mathematically, the ratio is determined by dividing the width by the height to find the common factor, which is then simplified into its lowest whole-number terms. This ensures that the geometric relationship remains constant regardless of whether the physical size is measured in inches, centimeters, or pixels.
The fundamental formula used to maintain proportions is based on cross-multiplication. To find a missing dimension while keeping an existing ratio, you multiply the target dimension by the ratio of the original sides. For example, if you know the desired width and the ratio, you divide the width by the first number of the ratio and multiply that result by the second number to find the height. This calculation ensures the image maintains its integrity without introducing distortion or stretching that would otherwise warp the visual content.
The most frequent mistake users make involves confusing resolution with aspect ratio. Resolution refers to the total number of pixels, such as 1920 by 1080, while the aspect ratio only defines the rectangular shape. People often assume that increasing the resolution automatically preserves the ratio, but changing one dimension without adjusting the other results in a different shape. Always treat the aspect ratio as a fixed constraint that dictates the required relationship between width and height before applying any changes to the resolution.