Free online OFF to BREP converter

What the OFF format is

OFF, or Object File Format, stores polygon meshes using a header, vertex coordinates, and polygon definitions. It is used for 3D geometry exchange, visualization, research datasets, and mesh-processing workflows.

OFF files commonly come from MeshLab, Geomview, academic geometry tools, and custom mesh-generation programs. The format normally contains no CAD history, feature tree, material data, units, or analytic surface definitions; some OFF variants also include vertex colors or normals.

What the BREP format is

BREP, short for boundary representation, describes a model through topological entities such as vertices, edges, wires, shells, and faces. A .brep file often refers to the Open CASCADE BREP representation, but BREP is not one universal interchange specification, so compatibility depends on the software that created it.

CAD systems use BREP for editing solids, checking topology, measuring geometry, and downstream operations such as Boolean cuts and fillets. Unlike OFF, a BREP can represent trimmed planes, cylinders, and other analytic surfaces, although a conversion from a mesh normally creates planar faceted faces instead.

How to actually convert OFF to BREP

Using FreeCAD

1. Open FreeCAD and switch to the Mesh workbench.
2. Choose File → Import and select the .off file. Inspect the mesh for holes, disconnected components, inverted normals, and self-intersections.
3. Switch to the Part workbench and select the imported mesh object.
4. Choose Part → Create shape from mesh. Set a tolerance appropriate to the model scale; an excessively large tolerance can merge nearby features, while an excessively small tolerance can leave fragmented or invalid geometry.
5. Select the resulting shape and choose File → Export. Select the BREP format and save the result with a .brep extension.
6. Reopen the exported file in FreeCAD or another Open CASCADE-based application and run its geometry or validity check before using it in manufacturing or Boolean operations.

For a file that contains only a clean closed mesh, this process generally produces a faceted shell or solid. If FreeCAD cannot create a valid shape, repair the OFF mesh first in MeshLab or another mesh-repair application, then repeat the import and shape-creation steps.

Using the online converter

You can also convert the file on 101convert.com for free without installing software: upload the OFF file, choose BREP as the output format when available, start the conversion, and download the generated file. Validate the downloaded model in the target CAD program because online conversion settings may not expose mesh-repair or tolerance controls.

Quality and compatibility limitations

OFF files generally do not define measurement units, so the imported model may need scaling. Record the intended unit before conversion and verify a known dimension afterward.

A mesh-to-BREP conversion does not usually reconstruct smooth NURBS or feature-based surfaces. A curved object represented by thousands of triangles becomes a BREP with many planar faces, which can produce a large file and slow Boolean, display, or machining operations.

Open shells, non-manifold edges, duplicate vertices, intersecting polygons, and reversed face winding can prevent creation of a valid solid. A successful export only proves that a BREP file was written; it does not prove that the result is watertight or manufacturable.

For editable CAD geometry, the preferred source is a native CAD file or a STEP/IGES export. Use OFF-to-BREP conversion when retaining the polygonal shape is acceptable.