STL to 3MF converter

To convert STL to 3MF, drop one or more STL files on the converter above and download the 3MF. Each STL becomes its own object in one project file, with millimetres written into the file, so Bambu Studio and PrusaSlicer open the whole set together. Nothing is uploaded.

Why turn STL files into a 3MF

STL describes a surface as triangles and nothing more. The Library of Congress format description calls it very limited, with no standard support for colour. A 3MF is a zip package defined by the 3MF Consortium, whose steering members include Microsoft, Autodesk, HP and Prusa Research. Its core specification records the unit in the file, allows many objects, and leaves room for colours, materials and slicer settings.

Converting gives you one tidy file for a multi-part model, the scale fixed in writing, and parts that stay separate so each can get its own filament.

What is inside the 3MF you download

The converter writes a core 3MF: a 3D/3dmodel.model file listing each part as its own object with shared vertices, one build item per part, and unit="millimeter". It carries no colours and no print settings, because STL had none. Your slicer adds those when you save the project from it.

Several STLs, one plate

When you drop several files, the converter places them side by side, 5 mm apart, so they do not overlap on the plate. Parts that came from one file keep their positions relative to each other.

Turn off Lay files side by side when the STLs were exported from one assembly, such as the colour layers of a multicolour model. They share coordinates, and keeping them in place means they stack back together correctly in the slicer.

Open it in your slicer

1. Bambu Studio: File > Import > Import 3MF/STL/STEP/SVG/OBJ/AMF, or drag the file in, then click Confirm in the loading dialog. This is Bambu Lab's documented route for standard 3MF files.
2. PrusaSlicer: press Ctrl+I to import, or Cmd+I on a Mac. Press A to arrange, which spreads the objects over the bed with a gap between them, per Prusa's help center.
3. Assign filaments, slice, and save the project. The saved 3MF then includes your settings.

Check the parts before you print

Every STL gets an edge check when it loads. A part with open edges may slice with gaps or fail outright; fix it in the STL repair tool first.

Other ways to make a 3MF

Any slicer that imports STL can save a 3MF: in PrusaSlicer, File > Save Project as writes all objects, settings and modifiers to one 3MF. The converter is quicker when you only need to bundle files, and it works without installing anything. To go back the other way, use the 3MF to STL converter, or open the result in the 3MF viewer to check it.