How to compute the missing dimension at a target aspect ratio

1. Source dimensions

   "Original width" and "Original height" are the source size in pixels (or any unit, as long as both match). Use them to define the ratio that must be preserved.

2. Target width

   "Target width" is the new width you want to fit. The tool will scale height proportionally. To target a height instead, swap width and height in all three fields — the math is symmetric.

3. Press Run

   Result returns targetHeight = Math.round(targetWidth × originalHeight / originalWidth). Result is rounded to the nearest integer pixel; sub-pixel precision isn't preserved.

4. Common ratio examples

   16:9 → from 1920×1080, target 1280 gives height 720. 4:3 → from 800×600, target 1024 gives 768. 1:1 → width and height are always equal.