PRJ to 3MF Converter
FileFlip converts PRJ to 3MF entirely inside your browser, using Assimp compiled to WebAssembly. The file is never uploaded to a server: it is read off your disk, converted on your own machine, and saved back by the browser. That means no file-size limit, no queue and no account.
How do I convert a PRJ file to 3MF?#
- Drop your PRJ file onto the converter at the top of this page, or click it to pick one from your computer. You can add as many as you like.
- Leave the target set to 3MF and the conversion starts on its own. FileFlip downloads 11.2 MB of WebAssembly the first time and nothing after that, then runs Assimp on your own machine.
- Save the 3MF file. Your browser writes it straight to your downloads folder, because there was never a server holding it.
Does converting PRJ to 3MF lose quality?#
Not in the sense of pixels or samples. Converting PRJ to 3MF rebuilds the file in 3MF's own model rather than re-encoding it, so everything 3MF can represent comes through exactly and anything it cannot has to be dropped. Expect the geometry to be exact, and anything the target has no place for, such as a rig, to be left behind.
Is it safe to convert PRJ files online?#
Yes, because nothing is uploaded. FileFlip converts PRJ files inside the browser tab you already have open, using WebAssembly builds of the same engines a desktop converter would install. Your file is read from your own disk into the page's memory, and no request carrying it is ever made.
You do not have to take that on trust. Open your browser's network panel, run a conversion, and you will see the engine come down and your file go nowhere. There is no upload, no server-side copy, no retention window, and no account tied to what you converted.
How FileFlip works lists every engine, its version and its download size, and shows how to check for yourself that nothing leaves your machine.
What PRJ to 3MF actually does to the file#
Converting PRJ to 3MF runs on Assimp, downloads 11.2 MB of WebAssembly the first time and nothing after that, rebuilds the file in the target's own model, and drops skeleton and animation.
| Engine | Assimp |
|---|---|
| Conversion path | One step: PRJ → 3MF |
| Downloaded to your browser | 11.2 MB, once, then cached by your browser |
| Quality | Rebuilt in the target's model |
| You get back | One file |
| Where it runs | In a background worker, so the page stays responsive |
What survives the conversion
| What is in the file | This conversion | Why |
|---|---|---|
| Materials | Sometimes | Survives for some files and not others. |
| Textures | Sometimes | Survives for some files and not others. |
| Skeleton and animation | Dropped | The target format has nowhere to put it. |
Worth knowing before you start:
- if the source carries a skeleton or animation, this target has no place to store it
What is a PRJ file?#
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.
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.
What is a 3MF file?#
A 3MF file is a ZIP archive of XML documents, published by the 3MF Consortium in 2015 as 3D printing's replacement for STL, adding the colour, material, unit and multi-object placement data STL never had.
Use 3MF over STL whenever colour, material or multiple positioned objects need to travel with the geometry to the printer.
Convert 3MF to STL only when the destination software is old enough to not support 3MF at all.
PRJ to 3MF 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.
What is a 3MF file?
A 3MF file is a 3D printing format, a ZIP archive of XML, published by the 3MF Consortium in 2015 to replace STL. It adds colour, material, real-world units and multiple objects with their placement on the build plate, none of which STL can store.