OBJ to STL Converter
FileFlip converts OBJ to STL 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 an OBJ file to STL?#
- Drop your OBJ 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 STL 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 STL file. Your browser writes it straight to your downloads folder, because there was never a server holding it.
Does converting OBJ to STL lose quality?#
Not in the sense of pixels or samples. Converting OBJ to STL rebuilds the file in STL's own model rather than re-encoding it, so everything STL 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 OBJ files online?#
Yes, because nothing is uploaded. FileFlip converts OBJ 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 OBJ to STL actually does to the file#
Converting OBJ to STL 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 materials, textures and skeleton and animation.
| Engine | Assimp |
|---|---|
| Conversion path | One step: OBJ → STL |
| 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 | Dropped | The target format has nowhere to put it. |
| Textures | Dropped | The target format has nowhere to put it. |
| Skeleton and animation | Dropped | The target format has nowhere to put it. |
Worth knowing before you start:
- the target stores triangles and nothing else, so materials, colours, and texture coordinates have nowhere to go
- if the source carries a skeleton or animation, this target has no place to store it
What is an OBJ file?#
An OBJ file is a plain-text 3D geometry format that Wavefront Technologies designed for its Advanced Visualizer software, storing vertex positions, texture coordinates and normals as human-readable lines of ASCII text.
Use OBJ when a static mesh needs to move between two different applications with the least risk of anything being misread.
Convert away from OBJ when the model needs animation, a skeleton, or to travel as a single file without a companion MTL.
What is an STL file?#
An STL file is a triangle mesh created by 3D Systems in 1987 for its stereolithography 3D printers, storing nothing but a flat list of triangle facets and their normals, with no colour, material or unit of measurement attached.
Use STL when the only destination is a 3D printer's slicer, which is all the format was designed to feed.
Convert STL to 3MF when colour, material or unit information needs to travel with the geometry, since STL has nowhere to put any of it.
OBJ to STL questions people ask#
What is an OBJ file used for?
An OBJ file stores the geometry of a single 3D model: its vertices, faces, texture coordinates and normals, written as plain text. It's used to move a static mesh between applications, since almost every 3D tool on every platform can read it.
Why does converting an OBJ file produce a ZIP?
An OBJ file only holds geometry; its material definitions, including which texture image goes where, live in a separate companion MTL file that the OBJ references by name. A converter has to hand back both files together, which is why an OBJ export comes as a ZIP rather than a single file.
Can OBJ files have animation?
No, OBJ has no concept of a skeleton, bone weights or keyframes, so it cannot store animation of any kind. It only describes a static mesh at one point in time; formats like FBX or glTF are needed for anything that moves.
Does OBJ support color and materials?
OBJ itself stores no colour or material data at all; that information lives in the companion MTL file it references, which defines diffuse and specular colours, transparency and texture maps using the Phong reflection model. Without the matching MTL file, an OBJ opens as a plain grey mesh.