PRJ File Format (.prj)
A PRJ file from 3D Studio is a project variant of Autodesk's chunk-based 3DS format, the same binary structure with a different top-level chunk marking it as a working project rather than an exported mesh.
PRJ at a glance#
| Full name | 3D Studio project |
|---|---|
| File extension | .prj |
| Category | 3D Models |
| Developer | Autodesk |
| First released | 1990 |
| Compression | Uncompressed |
| FileFlip support | FileFlip reads this format but does not write it |
What a .prj file can hold#
These are the things a PRJ file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Textures and materials | Yes |
|---|
Strengths and limitations of PRJ#
What PRJ does well
- Uses the same well-understood chunk structure as 3DS, so a 3DS-aware parser can read most of it directly
Where PRJ falls short
- The .prj extension is heavily overloaded; GIS software like ArcGIS uses it for coordinate-projection files that share nothing with 3D Studio's format
- Carries the same DOS-era 3D Studio limits as 3DS, including 65,536 vertices per mesh
- Support for the project-specific chunk data (lights and cameras) is inconsistent even among tools that read 3DS meshes fine
Use PRJ only when working directly in original 3D Studio DOS project files rather than their exported meshes.
Convert PRJ to OBJ or glTF to get the mesh into anything modern, since current tools target 3DS or newer formats rather than the old project files.
How to open a .prj file#
A .prj file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts PRJ into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Web | FileFlip |
PRJ questions people ask#
What is a PRJ file from 3D Studio?
A PRJ file is a 3D Studio DOS project, using the same chunk-based structure as a 3DS file but marked as the working project a 3DS mesh gets exported from, rather than the exported mesh itself.
Is a 3D Studio PRJ file the same as an ArcGIS PRJ file?
No, they're unrelated despite sharing an extension. A 3D Studio PRJ file is binary 3D scene data, while GIS software like ArcGIS uses .prj for a plain-text coordinate-system definition. The two need to be told apart by their source, not their extension.
What's the difference between a PRJ and a 3DS file?
Both use 3D Studio's chunk-based format, but a 3DS file is the exported mesh while a PRJ file is the working project, which can carry additional light and camera chunks that a plain 3DS export doesn't.
Converting PRJ files#
Convert PRJ to another format
FileFlip does not write .prj files, so nothing on the site converts into this format. It works as a source only.
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.