Convert STL to 3MF for Modern Slicers
Convert an STL into a 3MF package that Bambu Studio, PrusaSlicer, OrcaSlicer and Cura open directly. The shape comes across as one object in millimeters; check its orientation after import, because the current pipeline can deliver it lying on its back.
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Why Convert STL to 3MF?
STL stores a bare list of triangles with no units, no names and no idea of separate parts. 3MF is a ZIP package of XML that states its unit and can also carry colors, materials and slicer settings, which is why Bambu Studio and OrcaSlicer save their projects in it and why some print services and model sites ask for it.
On our servers the STL is read by Blender and saved as an intermediate GLB file; the mesh library trimesh then loads that mesh and writes the 3MF. The package holds a single mesh object, compressed with deflate, and declares millimeters as its unit, so the numbers in your STL are read as millimeters, the same assumption slicers make when they open an STL.
Shape and size come through, but the 3MF gains nothing the STL lacked: there were no colors, materials or settings to carry, so you add those in the slicer. There is one known problem. The GLB step uses a Y-up axis and the 3MF keeps it, so a part that stood upright in the STL can appear lying on its back after import. One 90 degree rotation around the X axis fixes it, and the slicer's lay-on-face tool works too.
Typical reasons for searching stl to 3mf: a print service or model-sharing site that accepts only 3MF, keeping a library in one format for Bambu Studio, or handing a model to someone with its unit stated. If you just want to print, every slicer named above opens the STL itself, and importing it there and saving the project also produces a 3MF that keeps your plate and settings.
How to convert STL to 3MF
- Check that the STL really contains triangles. A CAD export that failed can leave an empty file, and that is the usual reason this conversion stops.
- Upload one STL or several at once. Each file produces its own 3MF; multiple STLs are not combined into one project.
- Download the 3MF when the job finishes, which for typical files takes a second or two.
- Import it into your slicer and check the orientation; rotate it 90 degrees around X if it is lying on its back.
- Assign filaments, colors and print settings in the slicer, then save the project.
Key Conversion Features
- Writes a 3MF that declares millimeter units, matching how slicers read STL
- Reads both binary and ASCII STL
- Delivers a single mesh object ready for color painting and per-object settings
- Packs the model into the compressed ZIP container the 3MF format defines
- Converts a batch of STLs in one upload, each returned as its own 3MF
Video Tutorial
Pro tip: convert STL to 3MF without installing anything! 💡 🔗 https://miconvert.com/en/stl-to-3mf?utm_source=youtube&utm_medium=social&utm_campaign=stl-to-3mf ⏱️ Timestamps: 0:00 Intro 0:06 Finding
Frequently Asked Questions
Does Bambu Studio convert STL to 3MF by itself?
It can: import the STL, then save the project, and you get a Bambu project 3MF that also stores the plate and your settings. Use this converter when you want a plain 3MF without opening a slicer, or when you have a stack of files to convert.
Why is my model lying on its back after import?
The conversion passes through glTF, which treats Y as up, and the 3MF currently keeps that axis while slicers treat Z as up. Rotate the part 90 degrees around the X axis, or use the slicer's lay-on-face tool to put the correct side on the bed.
Will converting add colors or materials?
No. An STL has none to pass on, so the 3MF contains geometry only. Paint or assign filaments in your slicer after import, and save the project to keep them.
Does the geometry change?
The triangles are carried over, not remeshed or decimated; duplicate vertices that STL repeats for every triangle are merged into a shared list, which 3MF stores natively. Apart from the orientation issue above, size and shape stay the same.
Why did my STL fail to convert?
The usual message is that the imported model contains no exportable geometry. Blender opened the file and found no triangles, which happens with an empty or broken export. Open the STL in a viewer; if it shows nothing, export it again from the source program.
Is there a size limit for STL files?
Guests can upload STL files of up to 50 MB each; with a signed-in account the cap is 100 MB. Very dense scans are the files most likely to hit it.
Is my STL stored anywhere?
Only briefly. Our servers delete the uploaded STL when the job finishes, and the 3MF remains on the download page for around four hours until a cleanup job removes it.