Sometimes when you export a file from Revit, the file size dramatically increases. For example, a 30 mb Revit file can become 60 mb on export to FBX.
The original Revit file size is smaller because it contains less data than an FBX file. Revit scene file information accesses much scene information from libraries that reside within the Revit software, for example, Revit-specific construction data and textures. This information that is normally read from the Revit software now must be added on top of the FBX file on export so it can be reproduced accurately by software that cannot access Revit libraries.
This over-sizing problem also occurs with 3ds Max (.max) files on export for the same reason. A .max file must contain only the instructions that 3ds Max requires to create the scene. Materials and lighting information is read directly from the 3ds Max software libraries.
On top of this, when the Revit or 3ds Max file becomes an FBX file, it is converted to complex FBX scene information based on geometric data, such as vertex coordinates, UVs, and so on. This way, the FBX file contains the actual geometric data so it can be read in any software that supports the FBX format.
File sizes also tend to grow between Revit and FBX because all material data is embedded with the FBX file. The growth in file size means FBX files must contain every Revit texture used as materials so you can later import the FBX file into 3ds Max. A Revit scene file does not need to contain any texture files because the textures reside in the Revit software, where the scene file can refer to them.
Occasionally, large files do not import properly into 3ds Max due to memory constraints. If a file contains a massive amount of metadata and geometry, the import process can take hours.
There is also a known issue that affects few users when an extremely large FBX file is imported.
If you switch the 3ds Max System (not Display,) units to feet, so they match the Revit Imperial units exported to FBX, the import process takes much less time to complete. The unit conversion process is a complicated one for the FBX Importer and takes a long time to complete. Matching the units between an FBX file and the host program is often the deciding factor whether or not a large FBX file imports successfully into 3ds Max.
For more about System units conversion problems, see Unwanted scaling in 3ds Max.
