Free online DWG to BREP converter

What the DWG format is

DWG is AutoCAD’s native binary CAD format. It stores 2D geometry, annotations, layers, blocks, metadata, and—depending on the source—3D meshes, surfaces, and ACIS-based solid models. AutoCAD, BricsCAD, DraftSight, ZWCAD, and other compatible CAD programs create DWG files; engineering contractors commonly receive them for floor plans, mechanical layouts, site drawings, and 3D design data.

DWG is a drawing container rather than a single geometry type. A file containing only lines, arcs, dimensions, and text does not contain the topological faces and volumes required by BREP.

What the BREP format is

BREP, or boundary representation, describes a model through its topology and geometry: vertices, edges, trimmed faces, shells, and optionally solid volumes. The commonly exchanged .brep file is associated with Open CASCADE and is supported by applications such as FreeCAD and CAD systems using the Open CASCADE geometry kernel.

BREP is suitable for transferring precise 3D solids and surfaces for inspection, boolean operations, repair, simulation preparation, and downstream CAD processing. It preserves analytic geometry such as planes, cylinders, cones, and NURBS surfaces more directly than a polygon mesh, but it is not a universal interchange format and may not preserve DWG layers, dimensions, blocks, text, or drafting styles.

How to actually convert DWG to BREP

For an existing 3D DWG, use a CAD application that can read DWG and write Open CASCADE BREP. Rhino is a practical desktop option when its installed import/export filters support both formats:

1. Open the DWG in Rhino with File → Open. Select the correct DWG import units and version options.
2. Hide or delete 2D construction layers, annotations, blocks, meshes, and objects that should not enter the model.
3. Use Rhino inspection commands such as What, ShowEdges, and SelBadObjects to identify unsupported, open, or invalid geometry.
4. For a partial export, select the required solids and surfaces, then choose File → Export Selected. For the entire model, choose File → Export.
5. Choose Open CASCADE BREP (*.brep), if available in the file-type list, set the required export options, and save the file.
6. Open the resulting BREP in the target application and verify units, object count, closed shells, surface normals, and solid volume.

FreeCAD provides an alternative after the geometry is available in a format it can import. In FreeCAD, open the model, select the required Part workbench objects, then use File → Export and choose .brep or .brp, depending on the installed version. FreeCAD may not import DWG directly in every installation; converting the drawing to DXF first does not preserve DWG 3D ACIS solids reliably.

You can also use the free converter on 101convert.com without installing software when its DWG and BREP conversion is available for the file. Check the converted model in a CAD viewer because automated conversion cannot reconstruct missing 3D topology from a 2D drawing.

Quality and compatibility limits

The source geometry determines the result. A DWG containing closed 3D solids can usually be transferred with useful topology; a DWG containing disconnected wireframe entities requires surface creation, trimming, stitching, and solidification before export. Open shells may export as surfaces rather than solids.

Save a copy of the original DWG before conversion. Match the source and destination units explicitly, because BREP generally stores geometry but does not guarantee the same unit metadata conventions as DWG. Curved entities, proxy objects, custom objects, block instances, and unsupported ACIS features may be skipped or tessellated. Compare bounding-box dimensions and, for solids, calculated volume after import.