Convert STL to AMF

Why convert STL to AMF?

STL to AMF is occasionally needed for software and machines that ask for it by name, such as older Slic3r-based workflows, some research tools and industrial printers. AMF can store units, which STL cannot, so the output states millimetres explicitly and removes the usual guesswork about size. It is XML-based and normally compressed, so the file can also be smaller than an ASCII STL. The triangles are transferred exactly with shared vertices. Because the STL has no colours, materials or part structure, the AMF contains one plain object. If you only want a file that modern slicers prefer, 3MF is generally the better modern choice, as AMF support has been dropped from several programs.

How to convert STL to AMF

1. Drop your STL file onto the converter — it opens in your browser, nothing is uploaded.
2. Check the preview and the dimensions in mm; fix units or the up axis in “Units & orientation” if the size or orientation looks wrong.
3. Choose AMF as the output and click Convert. Several files download as one ZIP.

What carries over from STL to AMF

What changes

• Millimetres are stated explicitly, replacing STL's unspecified units.
• No colours or materials are added; STL contained none.
• Vertices are shared and the XML is compressed, so the file is often smaller than an ASCII STL.
• Geometry is unchanged; no remeshing is applied.

Tips

• Check that the target program really needs AMF; most current slicers prefer 3MF.
• Open the AMF in the target software to confirm that units and scale are right.
• Keep the STL as a fallback because AMF support varies between tools.

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 AMF files

AMF was standardised as ASTM F2915 and later ISO/ASTM 52915, with the aim of fixing the shortcomings of STL for additive manufacturing. A file is XML, optionally compressed as a ZIP, and describes one or more objects made of a vertex list and volumes of triangles. Unlike STL, it declares units, such as millimetre, inch or micrometre, and can attach colours and materials to volumes or even to individual triangles, with gradients between them. The specification also allows curved triangles, constellations that arrange several objects, and custom metadata. In practice it was overtaken by 3MF, which came from industry backers and gained support in Windows and the main slicers. AMF files still appear from some multi-material printers and research tools, and from older exporters in Cura, Slic3r and Meshmixer.

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.

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