Free online STL to 3MF converter

A slicer project, print workflow, or archive may require 3MF to retain units, multiple models, and application-specific print data that an STL cannot hold. Converting an STL also packages the mesh in a format used by current slicers such as PrusaSlicer, Bambu Studio, OrcaSlicer, and UltiMaker Cura.

What STL is

STL, originally associated with stereolithography, describes a model's outer surface as triangular facets. CAD users, modelers, 3D-printing repositories, and slicer users commonly exchange STL files because the format is simple and widely supported.

An STL may be ASCII or binary and stores mesh coordinates plus facet normal data. Standard STL does not define measurement units, colors, materials, textures, object structure, print settings, or editable CAD features. Most printing software interprets STL coordinates as millimetres, but that convention is not recorded in the file.

What 3MF is

3MF (3D Manufacturing Format) is a ZIP-based Open Packaging Conventions package for additive manufacturing. A .3mf file can contain one or more mesh objects, an explicit model unit, build-item transforms, and metadata; supported 3MF extensions can also store colors, materials, textures, components, and thumbnails.

Slicers commonly use 3MF as a project format. Their files can include plate layout, orientation, support or modifier objects, filament assignments, layer settings, and other slicer-specific data. Those settings are not defined consistently across every slicer, so a 3MF project saved in one application may not reproduce all settings in another.

Converting one ordinary STL creates a 3MF package containing the existing mesh and selected unit information. It cannot recover colors, materials, object hierarchy, print profiles, or parametric features that were never present in the STL.

How to convert the file

Use the free STL-to-3MF converter on 101convert.com when no desktop software is needed. Upload the .stl file, run the conversion, download the .3mf result, and open it in the intended slicer or receiving application to verify its size and geometry.

For a print project, import the STL into the slicer that will prepare the print, set the correct scale, orientation, plate position, materials, and print profile, then save its project as 3MF. In PrusaSlicer, use File → Import → Import STL, check the object dimensions, then select File → Export → Export plate as 3MF. In Bambu Studio, OrcaSlicer, and UltiMaker Cura, import the model, configure the plate, then use the relevant File → Save Project or File → Save Project As command.

On Windows, Microsoft 3D Builder can inspect and repair a mesh before export. Open the STL with Open → Load object, accept a repair prompt when required, confirm dimensions, then select Menu → Save as and choose 3MF.

Quality and compatibility checks

• Check units before saving. An STL designed in inches but imported as millimetres will be 25.4 times too small. Correct the scale before creating the 3MF file.
• Conversion does not add mesh resolution or fix geometry by itself. Faceted curves, holes, non-manifold edges, self-intersections, and inverted surfaces remain unless the selected application repairs them.
• Use a slicer's project-save command when settings must travel with the model. A generic conversion normally preserves geometry and basic 3MF data, not a complete slicer profile.
• Retain the original STL if a downstream printer, legacy slicer, CNC tool, or mesh editor accepts only STL. 3MF support is common in current printing software but is not universal.