Using the online template generator. I enter dimensions in MM but when the 3D model is generated, under "information" on the side it's in CM. When I export the OBJ and import it's also in CM.
This has been fixed in 3.1 beta: https://boxshot.com/2021/02/17/origami-3-1.html - please give it a try and let me know if it works for you there.
Customer support service by UserEcho