What is Aspect Ratio Calculator?
An aspect ratio describes the proportional relationship between a shape's width and its height, written as two numbers separated by a colon, such as 16:9. The numbers describe shape, not size - a 1920×1080 video and a 640×360 video both have a 16:9 aspect ratio. This calculator works in both directions: give it any width and height and it reduces them to the lowest-terms ratio and its decimal value, or give it a ratio plus the one dimension you know and it works out the other. Everything is computed locally in your browser, so nothing you type is sent anywhere.
Common Uses for Aspect Ratio Calculator
- Check what ratio a photo, video or screen resolution actually is
- Work out the height of a 16:9 video when you know the width
- Simplify odd ratios like 3440×1440 down to their lowest terms
- Plan a design or layout that must keep a fixed shape
- Convert between ratio form (16:9) and decimal form (1.778)
Two directions, one tool
Most aspect ratio problems are one of two kinds. First: 'what ratio is this?' - you have a width and height and want the ratio. Second: 'how big should it be?' - you have a ratio and one dimension and need the other. This calculator handles both: switch tabs to move between finding a ratio and finding a missing dimension, and use the preset buttons for common ratios like 16:9, 4:3 and 9:16.
How the simplification works
The calculator factors out the greatest common divisor of the two numbers. 3840×2160 divides by 240 to give 16:9. Decimal inputs are handled by scaling: 1.85:1 becomes 185:100, which reduces to 37:20. The result is the same shape expressed with the smallest possible whole numbers, which is what makes ratios easy to compare and reuse.
Why aspect ratio matters in practice
Mismatched ratios are the reason videos get letterboxed, photos get cropped and layouts break. If you place a 4:3 photo in a 16:9 frame without adjusting, something has to give: either the frame crops the photo, bars appear, or the image stretches and distorts. Knowing the ratio of your source and your destination up front lets you choose which trade-off to make deliberately.