Room volumes display on the Properties palette, in tags, and in schedules for rooms.
By default, Revit does not compute room volumes.
When volume computation is turned off, room tags and schedules display Not Calculated for the Volume parameter. Because volume computation may affect Revit performance, turn it on only when you want to prepare and print schedules or other views that report volumes.
Revit uses the Room component to maintain information about the area where it is placed.
Rooms store values for a variety of parameters that affect the heating and cooling for a project. An effective energy analysis can only be accomplished if all the areas in your model are defined by room components in the building model and the entire volume of the building model is included.
When project information is exported as an analytical model to a gbXML file, the volume for areas that are not typically considered as rooms in an architectural model must be included in the overall volume for the project. This includes spaces such as attics, shafts, chases, and the spaces between a ceiling and the floor above. Also, rooms in the building model should be defined to the center line of bounding walls and from floor height to floor height, so there are no gaps between the spaces in a building. You can examine a shaded 3D analytical model in the gbXML Export dialog to detect gaps. When there are gaps in the analytical model, you must adjust the room properties in the building model to correct the volume.