Aspect Ratio Calculator

An aspect ratio describes the proportional relationship between a shape's width and height, expressed as two numbers separated by a colon, such as 16:9 or 4:3. It matters anywhere a rectangle needs to be resized without distorting — video and photo dimensions, browser and device screens, print sizes, social media image specifications, and UI layout containers all rely on keeping a consistent ratio so that scaling something up or down does not stretch or squash it out of shape. The first thing this tool does is take any pixel width and height and reduce them to the smallest whole-number ratio that represents the same proportion — the same operation as simplifying a fraction. A 1920×1080 image, for instance, reduces to 16:9 because both numbers share a greatest common factor (GCD) of 120, and dividing both sides by that factor gives the smallest equivalent whole-number pair. This is exactly how the well-known standard ratios came to be known by their simple names: 16:9 for widescreen video, 4:3 for older television and monitor formats, 3:2 for most DSLR photo sensors, 1:1 for square formats like many social media profile images, and 21:9 for ultrawide monitors. The calculator performs this reduction with the standard Euclidean algorithm for finding a GCD, the same well-established method used across mathematics and computer science for this exact task. The second, reverse operation answers a different practical question: given a target ratio and one known dimension, what should the other dimension be? If you know a design needs to be 16:9 and must be exactly 1200 pixels wide, the matching height is 1200 × (9 ÷ 16) = 675 pixels. This comes up constantly in web and app design (fitting an image or video container to a specific ratio at a given width), in video production (matching resolution presets), and in print or physical media sizing. The tool lets you enter the target ratio, choose whether you know the width or the height, and it computes the other side for you instantly. Both calculations are pure arithmetic and require no external data or lookups, so everything runs the instant you stop typing, with results shown to a reasonable number of decimal places and trailing zeros trimmed for readability. Dimensions that are not whole numbers (a decimal width, for example) are still accepted for the ratio simplification, though the underlying GCD reduction rounds to the nearest whole pixel first, since a ratio expressed in fractional pixels is rarely a meaningful concept in practice.