Hex uses 1 unit = 1 cm, however it also has a rather small work area, the grid squares you see are 5 cm square and the whole grid area is 1 meter square, because of this what you thought was a large model might actually be tiny.
The right hand popout window has a Properties section, the Size is in centimeters, with your mesh selected you should see how big your mesh is with it.
Exporting is where your problems lie, as without knowing what the other programs 1 unit = ??? is means you’ll be messing about for a while trying to get the right scale.