Convert STL to 3MF
Free STL to 3MF converter that runs in your browser. See real dimensions before you download, and get a watertight, slicer-ready file.
Why convert STL to 3MF?
STL to 3MF is usually done to get a more capable file into a modern slicer. 3MF stores a unit, can hold several parts in one file and can keep colours, so Bambu Studio, PrusaSlicer, OrcaSlicer and Cura treat it as a project-friendly format. Some people also want a smaller, cleaner file than an ASCII STL, because 3MF is zipped. Be realistic about what the conversion adds: STL has no colours, units or part information, so the resulting 3MF contains the same geometry and nothing more. You gain the container, not new data. If you drop several STL files into the batch, each one becomes its own 3MF. The conversion happens locally in your browser.
How to convert STL to 3MF
- Drop your STL file onto the converter — it opens in your browser, nothing is uploaded.
- Check the preview and the dimensions in mm; fix units or the up axis in “Units & orientation” if the size or orientation looks wrong.
- Choose 3MF as the output and click Convert. Several files download as one ZIP.
What carries over from STL to 3MF
| STL | 3MF | Result | |
|---|---|---|---|
| Colour / materials | No | Yes | — |
| Textures | No | No | — |
| Units stored in file | No | Yes | Written as mm |
| Separate parts | No | Yes | — |
| Usual up axis | Z | Z | Unchanged |
What changes
- No new data appears: STL has no colour, material or part information, so the 3MF holds one grey mesh.
- The unit is written as millimetres, which matches what slicers assumed when reading the STL.
- File size is usually smaller than an ASCII STL because 3MF is compressed.
- Triangles and their order are preserved; nothing is remeshed or simplified.
Tips
- Open the 3MF in your slicer and check the size first; if it looks 25.4 times too large or small, the STL was probably in inches.
- To build a multi-part or multi-colour project, convert each STL and then combine them in the slicer.
- Use the free print check before slicing if the STL came from a download site and prints oddly.
About STL files
STL was created by 3D Systems in the late 1980s for its stereolithography machines, and it became the default exchange format for 3D printing. A file describes a surface as a list of triangles, each with three vertices and a facet normal. That is all it contains. There is no header field for units, no colour, no texture and no notion of separate parts. Two flavours exist: ASCII, which is readable text but large, and binary, which spends exactly 50 bytes per triangle after an 80-byte header and a 4-byte triangle count. Binary is what almost every modern tool writes. Because the format is so small and so old, every slicer, CAD package and mesh editor can read it, which is why hobbyists still download most printable models as STL from sites like Printables and Thingiverse.
About 3MF files
3MF was designed by the 3MF Consortium, whose members include Microsoft, Autodesk, HP, Stratasys and Prusa, as a modern replacement for STL in additive manufacturing. A .3mf file is a ZIP archive following the Open Packaging Conventions. Inside it, an XML model part holds the mesh, while other parts can hold thumbnails, textures and metadata. Unlike STL, the mesh shares vertices between triangles, which makes files smaller and keeps the surface connected. The core specification defines units, build items with placement transforms, and several objects in one file. Extensions cover materials, slices and beam lattices. Bambu Studio, OrcaSlicer and PrusaSlicer save their projects as 3MF with their own settings stored in extra files, so a project from one slicer may open in another with the geometry intact but the print profile ignored.
3D printing notes
For multi-colour and multi-part prints, 3MF is the format to use. Bambu Studio and OrcaSlicer open each part as a separate object, which lets you assign a different filament or setting to each one, and Prusa-family slicers do the same. Because the unit is stored in the file, a model does not arrive at the wrong size. Be careful with project files: a 3MF saved by Bambu Studio carries printer, plate and process settings that PrusaSlicer will not apply, and some slicers pick a different default when a model has no declared plate. MeshShift writes 3MF with several parts and keeps colours as base materials, and it reads 3MF for viewing, measuring and print checks.
Frequently asked questions
Is 3MF better than STL for printing?
For slicers that support it, mostly yes: it stores units and multiple parts and is compressed. For a single grey part the printed result is the same, because the geometry is identical.
Can I add colours when converting STL to 3MF?
Not in the conversion itself, since the STL has none to carry over. Paint or assign colours and filaments in your slicer after opening the 3MF.
Is this STL to 3MF converter free and private?
Yes. The conversion runs in your browser with JavaScript and WebAssembly, so your STL file is never uploaded to a server. There is no sign-up, no watermark and no daily limit; very large files are limited only by your device's memory.