Babylon’s world is in meters, so a unit of 1 is 1 meter.
You’ll want to make sure that Blender’s units is also set to meters if you want it to be 1:1. Otherwise you’ll have to do the scale conversion based on whatever you have set in Blender.
Here’s how you set the units in Blender:
Select the scene properties panel.
Then you can set the unit measurements accordingly. Here’s what I use to have a 1:1 representation in Babylon:
Unit Scale and Length are the things you’ll want to take into account.
Hope this helps!