You can calculate the aspect ratio of an image by entering the width and the height of the image. The aspect ratio is then calculated and generated in the grey box below the text inputs.
Second, you can calculate new image dimensions by changing either the height or width of the image. When the calculated width changes, the calculated height is generated using the aspect ratio and is displayed in the calculated height input.
The calculated inputs are bi-directional, meaning editing the calculated height would change the calculated width using the aspect ratio.