What is the 3DM file format?
.3dm is a 3D model format developed by Robert McNeel & Associates, used natively by Rhinoceros (Rhino) 3D software. A .3dm file stores 3D model data - surfaces, curves, points, and meshes - as well as metadata, layer definitions, and render attributes, all inside the openNURBS binary container.
.3dm is very versatile: it may be used to store and share 3D model data among many graphical programs and CAD, CAE, or CAM software. For that purpose, .3dm uses NURBS and polygon mesh representations. This allows users to exchange 3D geometry data among various devices and programs. .3dm files are chiefly used in manufacturing, production, and for interactive animations and games.
McNeel distributes the openNURBS toolkit (rhino3dm) as open-source C++, .NET, Python, and JavaScript libraries, enabling any app to read and write .3dm without a Rhino licence. Common companion formats include STEP and STL.
Security & safety
RISK: LOWA .3dm is geometry data, not an executable, so opening one in Rhino or a viewer is safe. Practical notes: .3dm files from complex models can be large; Rhino keeps a .3dmbak backup alongside the file. As with any download, get models from reputable libraries and beware disguised double extensions (model.3dm.exe).
Format details
in a nutshellFULL NAMERhino 3D Model (openNURBS)
DEVELOPERRobert McNeel & Associatessince 1990s (Rhinoceros); openNURBS file toolkit released publicly to let any app read/write .3dm
CATEGORY3D Image Files
MIME TYPEmodel/vnd.rhino.3dm
TYPEBinary 3D CAD model (NURBS surfaces, curves, meshes) - openNURBS container
STANDARDOpen · royalty-free
MAGIC BYTES · FILE SIGNATURE
OFFSET
00010203040506070809
HEX
334447656F6D65747279
ASCII
3DGeometry
A Rhino .3dm starts with the ASCII string "3D Geometry File Format " near the top of the file, followed by the binary openNURBS chunk structure. McNeel publishes openNURBS (now rhino3dm) as open C++/.NET/Python/JS libraries to read and write .3dm, so it is partly open.
Programs that open 3DM files
Windows3 apps
Rhinoceros (Rhino 8)
Paid Open the .3dm directly - Rhino is the native editor (90-day free trial available).
Autodesk Fusion
Freemium Use Insert/Upload to import the .3dm (via the Rhino import path) into a Fusion design. Free for personal/hobby use. 
macOS2 apps
Web2 apps
Rhino in browser / ShapeDiver / online 3DM viewers
Freemium Upload the .3dm to a browser-based viewer (powered by rhino3dm/Rhino.Compute) to spin and inspect the model without installing software.
3D-Tool Free Viewer
Freemium Open the .3dm to view, measure and analyze the model (free viewer; 14-day full trial). Technical details
deep spec| Developer | Robert McNeel & Associates |
| MIME type | model/vnd.rhino.3dm |
| File structure | Binary openNURBS chunk stream; file opens with the ASCII string "3D Geometry File Format" at byte offset 0, followed by typed binary chunks |
| Primary geometry | NURBS surfaces, trimmed surfaces, and NURBS curves - exact mathematical representation with no tessellation loss |
| Secondary geometry | Polygon meshes, point clouds, and SubD (subdivision surface) objects introduced in Rhino 7 |
| Coordinate system | Right-handed, Z-up; unit system and absolute model tolerance stored per file |
| Stored metadata | Named layers, render materials, embedded bitmaps, camera views, lights, and per-object plug-in user data |
| Block instances | Named block definitions with unlimited instances, enabling reusable instanced geometry within a single .3dm file |
| Annotation objects | Linear and radial dimensions, text objects, leaders, hatches, and dot annotations stored as first-class objects |
| Format versioning | Integer version number in the file header (e.g., 50 for Rhino 5, 60 for Rhino 6, 80 for Rhino 8); newer Rhino reads older file versions |
| Open toolkit | openNURBS / rhino3dm open-source SDK (C++, .NET, Python, JavaScript/WebAssembly) for third-party read/write of .3dm |
| Cross-platform support | rhino3dm library available for Windows, macOS, Linux, iOS, and Android; WebAssembly build enables in-browser use |
| Interoperability | Rhino imports and exports STEP, IGES, OBJ, STL, DWG, SKP, and others; .3dm is the native lossless round-trip container |
| Compression | No built-in compression; chunks store raw binary data; automatic backup copies are saved with the .3dmbak extension |
| Released | 1990s (Rhinoceros); openNURBS file toolkit released publicly to let any app read/write .3dm |
| Open standard | Yes · royalty-free |
| Specification | github.com |
3DM conversions
Possible
.3DM .DWGGUIDE
Yes - open the 3DM in Rhinoceros and export directly to DWG from File > Export Selected.
How to convert
.3DM .IGESGUIDE
Yes, 3DM can be converted to IGES - open the file in Rhinoceros and use File > Export > IGES, or import into…
How to convert
.3DM .OBJGUIDE
Yes - open the 3DM in Rhinoceros and export to OBJ via File > Export Selected.
How to convert
.3DM .STEPGUIDE
Yes, 3DM converts to STEP cleanly - the fastest way is File > Export in Rhinoceros and selecting STEP (.stp).
How to convert
.3DM .STLGUIDE
Yes - open the 3DM in Rhinoceros (or Autodesk Fusion) and export as STL; Rhino meshes the NURBS geometry…
How to convert
.3DM .STPGUIDE
Yes - open the 3DM in Rhinoceros or Autodesk Fusion and export as STEP/STP.
How to convert
.3DM .PDFGUIDE
Yes - open the 3DM in Rhinoceros and print or export the layout/view to PDF.
How to convert
.3DM .3DSGUIDE
Yes - open the 3DM in Rhinoceros and export directly to 3DS from File > Export Selected.
How to convert
Community Q&A
asked by usersNo questions yet - be the first to ask about 3DM files.
Frequently asked questions
How do I open a .3dm file without Rhino?
Use a free viewer: an online 3DM viewer (powered by rhino3dm), the 3D-Tool free viewer, or import it into Autodesk Fusion (free for personal use). For full editing you need Rhino itself.
What program makes .3dm files?
Rhinoceros (Rhino) by Robert McNeel & Associates - it's Rhino's native 3D model format, built on the open openNURBS/rhino3dm toolkit.
How do I convert a .3dm to STL for 3D printing?
Open it in Rhino (or import to Fusion) and Export/Save As STL - the NURBS surfaces are meshed into a printable STL. Check the mesh is closed/watertight before printing.
How do I get a .3dm into SolidWorks or Fusion?
Export the .3dm from Rhino to STEP (.stp) or IGES - those neutral formats preserve solids/surfaces and import cleanly into most mechanical CAD.
Is .3dm the same as 3DML?
No - that's a mix-up. .3dm is the Rhino 3D Model. '3DML' (Flatland's 3D Markup Language) was an unrelated, long-dead web format. Treat .3dm as Rhino geometry.
Can I open a .3dm on my phone or in a browser?
Yes - browser-based viewers built on rhino3dm/Rhino.Compute let you upload and spin a .3dm with no install, which also works from a phone for quick viewing.
References
1Rhinoceros - official site (McNeel)www.rhino3d.com
2openNURBS / rhino3dm - read & write .3dm (open libraries)github.com
