Free online 3DM to BREP converter

Applications based on Open CASCADE or other CAD kernels may require a .brep model instead of Rhino's native .3dm file. Converting is useful when transferring editable boundary-representation geometry to engineering software, simulation tools, or a CAD archive.

What the 3DM format is

.3dm is the native file format of Rhinoceros (Rhino), developed by McNeel. It stores NURBS curves, surfaces, solids, meshes, annotations, layers, blocks, materials, and scene settings. Rhino and Grasshopper workflows commonly produce 3DM files, and they are also used by jewelry, product-design, architecture, and fabrication software that supports Rhino geometry.

A 3DM file can contain several object types at once. Some objects may be closed solids, while others are open surfaces, meshes, curves, or construction geometry.

What the BREP format is

BREP, or boundary representation, describes a model through its topology and boundary geometry: vertices, edges, faces, shells, and solids. A .brep file commonly refers to the Open CASCADE BREP representation, although “BREP” can also describe an internal model structure without identifying one universal file standard.

BREP is suited to CAD and geometry-processing applications that need exact faces and topology rather than a polygon mesh. It preserves analytic and NURBS surfaces more accurately than STL or OBJ, but usually carries less project information than 3DM, such as layers, materials, lights, annotations, and Grasshopper data.

How to convert 3DM to BREP

Using Rhino

1. Open the .3dm file in Rhino.
2. Check the model with Analyze → Edge Tools → Show Edges and confirm that intended solids are closed. Repair gaps before export with commands such as _ShowEdges, _Join, or _Cap where appropriate.
3. Select the objects to export. Use File → Export Selected when the file contains construction geometry or objects that should not be transferred.
4. Choose Open CASCADE BREP (*.brep) in the file-type list and save the output, for example as model.brep. In Rhino versions that expose the format through the command line, run _Export and select the BREP file type.
5. Accept the export options, then open model.brep in the target CAD application and run its geometry or topology check.

Using the built-in online converter

You can convert the file for free on the 101convert.com website without installing software. Upload the 3DM file, choose BREP as the output format, start the conversion, and download the generated .brep file. Use a desktop CAD application instead when the model is confidential or requires repair and validation before export.

Quality and compatibility limits

BREP export transfers boundary geometry, not the full Rhino document. Layers, display modes, render materials, dimensions, annotations, Grasshopper definitions, and unsupported object types may be omitted.

Units are a frequent source of errors. Confirm the Rhino model units under File → Properties → Units and verify the import scale in the destination program; BREP files may not communicate unit metadata consistently between applications.

Open or invalid Rhino surfaces can remain open shells in the BREP output. A target program may reject them when it expects a watertight solid. Meshes and SubD objects may require conversion to NURBS or another supported boundary type before export, which can increase file size or alter curvature.

BREP compatibility depends on the receiving CAD kernel and its version. If direct BREP import fails, export from Rhino to STEP instead; STEP generally provides broader interoperability but may not preserve every Rhino-specific object or modeling detail.