Package a triangle mesh as a 3MF model with one geometry object and an explicit millimetre unit. Review the free preview and independent saved-file checks before downloading.
A focused format conversion
STL and 3MF both represent triangle mesh geometry, but 3MF can also declare units and store build information and appearance resources. This converter writes the STL's mesh as one 3MF object and one build item. It does not split the mesh into separate objects based on disconnected shells because STL does not identify assemblies or object boundaries reliably.
The output model explicitly declares millimetres. The converter packages the geometry in a 3MF archive, then a separate QA reader opens the saved archive and checks its model XML, triangle coordinates, object count, unit declaration and dimensions against the saved STL input. A preview is built from the independently parsed 3MF result.
STL coordinates have no reliable unit
An STL file contains coordinates but has no standard unit field. A coordinate value of 25.4 might mean millimetres, inches or another scale depending on the application that created the file. This tool assumes that the STL coordinates are already millimetres and records that assumption in its QA output. It does not attempt to infer physical scale from the shape.
If the model looks too small or too large in the preview, check the intended dimensions in the source application before continuing. Changing scale as part of a format conversion would alter geometry; this tool instead preserves the numeric coordinates and labels the new 3MF unit as millimetres.
One geometry object, without invented appearance
The resulting 3MF contains one mesh object and one build item. Separate disconnected regions in the source may remain separate triangle islands inside that mesh, but they are not promoted to an assembly with individual identities. This predictable structure is useful when an application expects a single model and avoids inventing object names or hierarchy that the STL never supplied.
STL also carries no standard colors, materials, texture maps, texture coordinates or CAD history. The converter does not invent those properties. The 3MF contains geometry and its millimetre declaration; it cannot recover appearance or design information absent from the source.
Independent verification of the saved archive
The payment gate does not rely on the converter's in-memory measurements as proof. It reopens the saved STL input and the saved 3MF output with separate readers, compares all triangle corner coordinates while ignoring facet order and winding, verifies that the result has one mesh instance, checks its unit and compares the bounding dimensions. Invalid archives, changed facets, missing geometry or a wrong unit declaration fail verification.
The preview is derived from the parsed saved 3MF only after the geometry checks pass. If verification fails, no paid download is offered. If QA reports that the STL unit was assumed, that is an explicit statement about the source format rather than a claim that STL declared millimetres.
When to use 3MF
Choose 3MF when your target application supports the format and you want a ZIP-based model with a declared unit and room for richer build or appearance data in later workflows. It is not a replacement for native CAD: a triangle surface does not restore sketches, constraints or editable feature history. Keep the STL source until you have opened the 3MF in the target application and confirmed scale and orientation.
For the opposite conversion, use 3MF to STL, which applies build placements and declared units and reports appearance data that STL cannot retain. You can inspect a local 3MF in the browser viewer without uploading it, or read the 3MF file guide for an overview of model resources, builds and unit handling.
Frequently asked questions
What unit does the output 3MF declare?
The output explicitly declares millimetres. QA independently checks that the saved model includes this unit.
What units are assumed for the STL input?
STL has no standard unit metadata, so its coordinate values are treated as millimetres. The assumption is shown in the QA report.
Will the output contain multiple objects?
No. The whole STL mesh is written as one 3MF geometry object and one build item, including any disconnected triangle islands.
Does the conversion add colors or materials?
No. STL does not carry standard appearance data, so the resulting 3MF contains no invented colors, materials or textures.
How is the saved result checked?
A separate reader reopens both files and compares their triangle coordinates, dimensions, unit declaration and object count. The preview is generated from the saved 3MF.