Hey, these are dimensions in isometric 3D space. Left and Right dimensions are measured in 2px units, and the Height of the box is just 1px unit
I believe, calculating 2D width would look like this: (Left × 2) + (Right × 2) + 2
The height is a bit tricky though, and would probably envlove some logic.
The main idea behind this script is thinking in isometric space in terms of units, instead of 2D plane and pixels