Zoom aspect ratio calculator
Original size
Scale to a new size (keeps the same ratio)
The ratio is exact - found with the greatest common divisor, not rounded to the nearest common name. Zoom, video calls and slides are built around a small set of standard ratios (16:9, 4:3, 1:1); a background or slide sized to the wrong ratio gets cropped or letterboxed by the platform.
Two related jobs in one tool
First, it simplifies any width and height into a named ratio - a 1920x1080 image is exactly 16:9; a photo at 4000x3000 is exactly 4:3 - using the greatest common divisor rather than rounding to the nearest common ratio, so the result is exact, not an approximation dressed up as a name.
Second, given a target width or height, it works out the other dimension that keeps the same proportions - the calculation behind "resize to 1280 wide, keep it proportional" that an image editor does silently, made explicit so it can be checked or used before the file is even opened.
Why this matters for calls and screen shares
Zoom, video calls and presentation slides are built around a small set of standard ratios (16:9, 4:3, 1:1) - a virtual background or slide sized to the wrong ratio gets cropped or letterboxed by the platform rather than shown as designed. Checking the ratio before uploading catches this before it surprises anyone mid-call.
Related tools
See the Zoom virtual background resizer to resize an actual image file to a target ratio, not just calculate the numbers.
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