Nice function.
I would recommend to use a more configurable approach using the base size of the html for converting, using the unit in the value for converting and output errors if input is wrong.
You can see my suggestion here https://gist.github.com/npostulart/4de142bf2874c1802a15
I didn’t updated the pt convert part yet as I need to figure out the correct values for converting.
Hope you like my changes to your code.