Aspect Ratio Calculator
Reduce a width and height to its simplest aspect ratio.
Enter a width and height in pixels (or any units) and this tool reduces them to the simplest whole-number aspect ratio, such as 16:9 or 4:3. Handy for video, images, screens and design work where you need to keep proportions consistent.
Formula / method
Examples
16:9
5:4
How the ratio is reduced
Given a width and a height, the tool finds their greatest common divisor (GCD) and divides both numbers by it, leaving the pair in lowest terms. For example, 1920 and 1080 share a GCD of 120, so 1920x1080 collapses to a clean 16:9. It is the same arithmetic our Simplify Fractions tool uses, just applied to two screen dimensions instead of a numerator and denominator.
Because the ratio is exact, it only simplifies when the numbers share common factors. Something like 1366x768 does not reduce to a tidy 16:9 (it is really 683:384), which is a useful hint that a resolution is not a perfect match for a standard ratio.
Where aspect ratios matter
Aspect ratio describes shape independent of size, so 16:9 looks identical whether the image is 1280 pixels wide or 3840. Common ones include 16:9 (widescreen video and most monitors), 4:3 (older displays and slides), 1:1 (square social posts), 9:16 (vertical phone video), 3:2 (many cameras), and 21:9 (ultrawide). Knowing the ratio lets you scale media without stretching or cropping.
Where it's used
- Reducing a screen resolution to check if a monitor is a true 16:9 panel
- Sizing video exports for YouTube (16:9), Instagram (1:1 or 4:5) or Reels and TikTok (9:16)
- Scaling an image up or down without stretching or squashing it
- Choosing crop dimensions for a print, banner or thumbnail
- Confirming a camera's photo ratio such as 3:2 or 4:3
Real-world examples
- 1920 x 1080 reduces to 16:9, the standard widescreen ratio
- 1280 x 1024 reduces to 5:4, revealing the panel is not a true 16:9
- 1080 x 1080 reduces to 1:1, a square social-media post
A bit of history
The 16:9 widescreen ratio was proposed in 1984 by Kerns Powers of the SMPTE, who found it is the geometric mean of the era's common formats and a shape that could contain both 4:3 television and wide cinema frames; it was later adopted as the HDTV standard.
FAQ
What is the most common aspect ratio?
16:9 is the standard for monitors, TVs and online video. 4:3 is the older "square-ish" format, and 21:9 is ultrawide.