In one line
CAD, computer-aided design, is a way of drawing. BIM is a way of building a digital version of the building itself. A CAD drawing of a wall is lines. A BIM wall is an object that knows its height, thickness, material and fire rating, and which level it stands on.
Side by side
| CAD | BIM | |
|---|---|---|
| What it makes | Drawings: lines, arcs and text | A model: objects with data |
| Dimensions | 2D or plain 3D geometry | 3D objects with real sizes |
| Changes | Edit each drawing separately | Change once; every view updates |
| Quantities | Counted from drawings by hand | Generated from the model |
| Coordination | Overlay drawings and compare by eye | Run automated clash tests |
| After construction | Drawings archived | Model can support operations |
When 3D CAD is enough
If the deliverable is a set of drawings for a small, simple job, and nobody downstream needs data from the model, CAD can be quicker and cheaper. Plenty of small works are still drawn this way.
When BIM is worth it
- Several trades share a crowded space, such as a ceiling void full of ducts and pipes.
- The owner, authority or contractor requires BIM or an open IFC model.
- You need accurate quantities for cost planning.
- You are renovating an existing building and need an as-built model from a scan.
- The building will be operated for decades and a good record of it is valuable.
Converting CAD to BIM
If you already have CAD or PDF drawings, they can be converted into a BIM model. The quality of the model depends on the quality of the drawings, so we log every assumption we have to make and ask you to confirm it. See our BIM modeling service.
Published 14 October 2026 · Written by the Sactik team