At first glance, it might seem that the main component of BIM is that it is conveyed in 3D. Therefore, a common question is what makes BIM any different from 3D CAD.

If you're asking this question, here's your answer: BIM is not 3D CAD.

To properly understand, it's important to begin with this question: What is BIM?

Building Information Modeling is a process for designing, constructing, and maintaining buildings digitally. It is used by architects, engineers, contractors and building owners for holistic building design & project collaboration.In a BIM workflow, instead of drawing lines that represent walls or doors, architects just draw walls and place doors. And while a CAD door modeled in 3D and a BIM door may look very similar if you were to open them side by side, the difference is in the data.

BIM content is also defined by data. In a BIM project, everything has metadata – information about size, square footage, material makeup, fire rating, finishes, manufacturer, even mechanical, electrical, and plumbing connections.

The other hallmark of BIM is that the components are parametric. This means that architects no longer have to stretch (or scale) the door drawing that was provided by the manufacturer to all the different sizes the door comes in – all the options are built into the component and can be selected quickly and simply by the architect. This ensures accuracy and speed.

On the CAD side, 3D CAD is a file type that helps architects by being visible in plan, elevation, section, and 3D in AutoCAD. 

If AutoCAD is essentially a digital version of what Architects have always done – draw lines – 3D CAD is just 3D lines.

With the increasing interest of the AEC community in BIM, some software developers have started to put BIM-light functionality into their legacy software. Autodesk, the company that makes Revit and AutoCAD, has started to try to sell AutoCAD as BIM software by adding more functionality like 3D CAD.  However, the difference in capability and purpose - for the time being - is significant.