Generally speaking, if the PPI (pixels per inch) of your device is 96, you can just use the following fomula to calculate the peixl.
Pixel = inch * PPI/DPI
Notes: PPI/DPI are essentially the same concept that how many dots exits in a inch.
While in Powerpoint, by default, the measurement unit is inch. But in Powerpoint VBA, the unit of height/width is Point. If you want to convert inch to Point, you can just multiply 72.
Point = Inch * 72
It’s pretty simple.