Find the ratio from any dimensions, or calculate a missing dimension from a known ratio. Visual preview included.
Fill in any one of the width or height fields to compute the other.
The Aspect Ratio Calculator turns any width and height into its simplest ratio, and works the other way too — give it a ratio plus one dimension and it computes the missing side instantly.
Every change updates live, including a scaled visual preview of the shape, so you can see exactly how 16:9 differs from 4:3 or 1:1 at a glance. People reach for it to:
It runs entirely in your browser, so nothing is uploaded and there is no sign-up — just type a dimension and read the answer. The calculator loads pre-filled with 1920x1080 so you immediately see a worked 16:9 example.
Whether you are cropping a banner, prepping a thumbnail, or matching a video to a platform spec, getting the ratio right keeps proportions intact. Bookmark it as a quick reference any time you need to scale dimensions and keep everything looking the way it should.
An aspect ratio is the proportional relationship between an image or video width and height, written as W:H (for example 16:9). It describes the overall shape regardless of the actual pixel size, so a 1280x720 image and a 1920x1080 image share the same 16:9 ratio.
1920x1080 is 16:9, the standard widescreen ratio used for Full HD video, most TVs, monitors, and YouTube. Dividing both numbers by their greatest common divisor of 120 gives 16 by 9.
16:9 is the modern widescreen standard used for HDTV, YouTube, and almost every modern display. 4:3 is the older, nearly square standard used by classic TVs and computer monitors before the 2000s. Switching content between the two leaves either black bars or a cropped image.
Keep the same aspect ratio as the original. Enter your target ratio, type the new width or new height, and let the calculator fill in the matching dimension. Because both sides scale by the same factor, the image keeps its proportions and nothing looks squashed or stretched.
16:9 is by far the most common video aspect ratio. It is the default for YouTube, broadcast HD, streaming, and most cameras. Vertical 9:16 has become standard for short-form mobile video such as Reels, TikTok, and Stories.
Divide both the width and height by their greatest common divisor to get the simplest whole-number ratio. This tool does it automatically the moment you enter any two dimensions, and also names the ratio if it matches a common standard.
Use 1:1 square or 4:5 portrait for Instagram feed posts, 9:16 vertical for Reels, TikTok, and Stories, and 16:9 widescreen for YouTube and most landscape video. Matching the platform ratio avoids awkward cropping and keeps your content looking intentional.