Use this STL to 3MF converter to move a plain triangle mesh into the file type used by many newer slicers and 3D printing apps. It creates a simple, single-object 3MF without uploading your model. It is useful when a workflow asks for a .3mf file but the model you have is an STL.
Move an STL into a modern 3MF workflow
STL is still widely supported, but it stores little more than the model's surface triangles. A 3MF file is a package that can hold a mesh along with richer printing data. Converting the STL gives you a valid 3MF container that is easier to use in a 3MF-based workflow.
| Data the format can hold | Standard STL | 3MF |
|---|---|---|
| Triangle mesh geometry | Yes | Yes |
| Declared model units | No | Yes |
| Colors and materials | No | Yes |
| Texture images | No | Yes |
| Reliable named objects and components | No | Yes |
| Build-plate placement | No | Yes |
| Thumbnail or preview image | No | Yes |
| Printer and slicer settings | No | Possible in slicer-created 3MF projects |
| Built-in file compression | No | Yes |
You can open the converted file in your slicer and add the printer, filament, support, and plate settings you need.
What this converter actually puts inside the 3MF
The triangle mesh stays the same
The converter reads ASCII and binary STL files. It copies the source triangles into one mesh object inside the 3MF package. It does not smooth the surface, add detail, or change the shape.
The only optional geometry change is the small-model scale choice shown during import. If you choose Scale to millimeters, the tool multiplies every coordinate by 1000 before writing the 3MF.
Colors, print profiles, and build plates are not added
The 3MF format can store colors, materials, thumbnails, build plates, and slicer settings. A normal STL does not contain that information, so this converter has nothing to carry over. The downloaded 3MF contains geometry only.
You can still add colors and print settings after opening the file in Bambu Studio, OrcaSlicer, Cura, PrusaSlicer, or another compatible app. Those changes come from the slicer, not from the conversion.
Check the model size before downloading
Why STL files cause unit surprises
STL coordinates do not include a reliable unit. One program may write a value of 1 to mean one millimeter, while another may mean one meter or one inch. The geometry can be correct but appear much too small or too large when another app opens it.
Check the dimensions shown in the preview and check them again in your slicer. If you are not sure what size the source should be, inspect it first with the Free Online STL Viewer.
When to use Scale to millimeters
Use Scale to millimeters when the model looks much smaller than expected in the preview. You can usually spot this by looking at the model in the viewer and checking its displayed dimensions. The option multiplies every coordinate by 1000, which corrects an STL that was exported in meters but needs to be read as millimeters.
Keep the original size if the model is meant to be very small. If it was exported in inches, also keep the original size here and apply a 25.4 scale factor in your modeling software or slicer instead.
A new file format cannot repair a damaged mesh
Changing the container does not close holes, remove self-intersections, fix flipped faces, or make a non-manifold model watertight. These problems can still cause missing layers or failed toolpaths after conversion.
Rotate the preview and look for missing or unexpected surfaces. Then let your slicer run its normal mesh checks before printing. Repair the STL in a mesh editor when the source geometry is broken.
When to keep the 3MF and when to keep the STL
Keep the 3MF when a slicer, upload form, or shared workflow asks for that format. It is also a good starting point if you plan to add slicer-specific settings and save a richer project later.
Keep the original STL as the source copy. This converter does not add information that makes the new file a better master model. If you need a plain mesh again, use the Free 3MF to STL Converter, but remember that colors, materials, textures, thumbnails, build-plate layout, print profiles, and other slicer settings do not transfer to the STL.
Open the converted file in your slicer next
Open the downloaded 3MF and confirm its dimensions, orientation, and first-layer contact. Add your printer profile, filament, layer height, infill, supports, and plate layout there. If you need G-code from the original mesh, the Free STL to G-code Converter can create a starting file, but always review machine code in your printer software before printing.