Convert 3MF to STL
Free 3MF to STL converter that runs in your browser. See real dimensions before you download, and get a watertight, slicer-ready file.
Why convert 3MF to STL?
Most people convert 3MF to STL because something downstream only understands STL: an older slicer, printer firmware with a fixed file list, a print service's upload form, or a CAD or mesh-repair tool that never learned 3MF. A project saved from Bambu Studio, PrusaSlicer or Cura carries more than geometry, so the question is what you actually need to keep. The mesh itself survives untouched. Colours, per-part settings and the plate layout do not, because STL has no place to store them. If your 3MF holds several parts, they are written into a single STL as one mesh. Run this in the browser and the file never leaves your computer.
How to convert 3MF to STL
- Drop your 3MF 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 STL as the output (binary is smaller; ASCII is human-readable) and click Convert. Several files download as one ZIP.
What carries over from 3MF to STL
| 3MF | STL | Result | |
|---|---|---|---|
| Colour / materials | Yes | No | Dropped |
| Textures | No | No | — |
| Units stored in file | Yes | No | Numbers in mm |
| Separate parts | Yes | No | Merged into one mesh |
| Usual up axis | Z | Z | Unchanged |
What changes
- Colours and base materials are dropped; STL stores triangles only.
- Multiple parts or objects are merged into one mesh, so you lose the ability to select them separately.
- Slicer-specific data such as print profiles, supports painted in the project and plate positions is not part of the geometry and is not carried over.
- Units are not recorded in STL; the size is written in millimetres, which is what slicers assume.
Tips
- If the 3MF has several objects you want to print separately, convert them one at a time or export each object from your slicer first.
- Check the dimensions shown before converting; they should match the size you saw in the slicer.
- Run the free print check afterwards if the STL will go to a service that rejects non-manifold meshes.
- Keep the original 3MF as your editable master and treat the STL as a delivery format.
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.
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.
3D printing notes
STL is still the safest file to hand to a slicer. Bambu Studio, PrusaSlicer, OrcaSlicer, Cura and the resin tools Chitubox and Lychee all import it, and they all treat the numbers as millimetres. The usual problems are scale (a model exported from a metre-based tool arrives 1000 times too small) and meshes that are not watertight, which makes slicers fill or skip regions. MeshShift shows the real dimensions before you convert and can scale from metres automatically. Its print check lists holes, non-manifold edges and flipped normals, and one click rebuilds a closed solid at the same size. If you need colours or several plates in one file, use 3MF instead.
Frequently asked questions
Will my colours survive converting 3MF to STL?
No. STL cannot store colour or material data, so the output is a single grey mesh. If you need colours later, keep the 3MF, or choose a format that carries them such as OBJ, PLY or GLB.
Why does my slicer show the STL at a different size?
STL has no unit field, so slicers assume millimetres. A 3MF stores its unit, and the converter writes millimetres, so sizes should match. If they differ, check the dimensions shown before conversion.
Is this 3MF to STL converter free and private?
Yes. The conversion runs in your browser with JavaScript and WebAssembly, so your 3MF 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.