Aspect Ratio Calculator

An aspect ratio expresses the proportional relationship between a rectangle's width and height as two whole numbers separated by a colon. A 16:9 frame is 16 units wide for every 9 units tall. The ratio stays the same whether the frame is 1280x720 or 3840x2160, so it describes shape, not size.

16:9 is the standard for YouTube, most streaming platforms, TV broadcasts, and desktop monitors. Use 9:16 for vertical mobile content like Instagram Reels, YouTube Shorts, and TikTok. Use 1:1 for square Instagram feed posts, and 21:9 for cinematic ultrawide footage.

Set the ratio first, either by typing values into the Ratio W and Ratio H fields or by tapping a common ratio like 16:9. Then enter only one dimension, the width or the height, and clear the other. The calculator derives the missing dimension from the ratio and rounds it to the nearest whole pixel, so proportions are preserved.

3:2 matches most DSLR and mirrorless sensors and is the native ratio for standard 4x6 prints. 4:3 is the native ratio for Micro Four Thirds cameras and most smartphone sensors. 1:1 works well for Instagram posts and album covers. The right choice depends on your camera sensor and intended output size.

The calculator divides both dimensions by their greatest common divisor (GCD). A 1920x1080 frame shares a GCD of 120, so it simplifies cleanly to 16:9. A 1366x768 frame has a GCD of only 2, reducing to 683:384, because those pixel counts are not exactly proportional to any small ratio. For a clean ratio like 16:9, you need pixel dimensions that are exact multiples of both numbers.