STL Converter
FileFlip converts STL files into 13 other formats entirely inside your browser, using Assimp compiled to WebAssembly. The STL file is never uploaded to a server: it is read off your disk, converted on your own machine, and saved back by the browser. There is no file-size limit and no account to create.
How do I convert an STL file?#
- Drop your STL file onto the converter at the top of this page, or click it to pick one from your computer.
- Choose the format you want out of it. FileFlip downloads the engine that conversion needs, once, and your browser caches it.
- Conversion starts the moment you pick the format, and the result is yours to download. The work happens in this tab, so nothing is uploaded and nothing is queued.
Is it safe to convert STL files online?#
Yes, because nothing is uploaded. FileFlip converts STL 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 happens to a STL file#
FileFlip converts STL into 13 formats with Assimp, all of it inside the browser tab. Each conversion below names the engine it uses, what it downloads, and exactly what that conversion keeps or drops.
| Category | 3D Models |
|---|---|
| File extension | .stl |
| FileFlip support | Read and written |
| Conversions available | 13 |
| Engines | Assimp |
| Downloaded to your browser | 11.2 MB on the first conversion, then cached |
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.
The STL file format reference covers the specification, the programs that open one, and what each conversion keeps or drops.
STL questions people ask#
What is an STL file used for?
An STL file is the standard input for 3D printer slicing software, storing a model's surface as a list of triangles with nothing else attached. Slicers use it to work out where to lay down material layer by layer.
Why doesn't my STL file have color?
STL was designed in 1987 purely to describe a shape for stereolithography printing, so it never included fields for colour, material or texture, only triangle geometry. 3MF was created later specifically to add colour and material data that STL can't hold.
What's the difference between ASCII and binary STL?
ASCII STL spells each triangle out as readable text starting with 'solid' and ending with 'endsolid', while binary STL packs the same triangles into a compact format with an 80-byte header followed by a triangle count and raw floating-point data. Binary STL is far smaller and is what most software writes by default.
What units does an STL file use?
STL has no built-in unit of measurement; every coordinate is just a number, and the software producing or consuming the file has to agree separately on whether it means millimetres, inches or something else. Importing an STL into the wrong unit setting is a common cause of a model coming out the wrong size.