Free STL to 3MF Converter
Drop an STL file below to save it as a 3MF that states its unit. Your file is never uploaded.
Your files never leave your browser. Nothing is uploaded.
What are STL and 3MF files?
STL is the plain format of 3D printing. It stores a model as a list of triangles and nothing else: no colors, no textures, and no unit. Slicing programs and CAD tools all read it.
CAD apps such as Fusion and Onshape export STL, and so does Blender. Model sites such as Thingiverse and Printables list printable models as STL.
3MF is a 3D printing format from the 3MF Consortium. It is a zip file that holds the model as XML. Unlike STL, it states its unit, and it can hold colors and several parts.
3MF is a newer alternative to STL. Slicers read it, it states its unit, and it keeps a color for each part.
How to convert STL to 3MF
Step 1. Drop your STL file on the converter above, or choose it from your device.
Step 2. Look at the preview. If the model lies on its side, change the up direction to match your file.
Step 3. Check the unit. STL does not say which unit it uses. Slicers read it as millimeters, so that is the starting choice here. Choose the unit your model was made in, and the 3MF file is scaled to millimeters. The size next to the download button changes with it.
Step 4. Press the download button. The 3MF file is saved to your device, named like your original with .3mf at the end.
Moving from STL to 3MF
3MF was made to replace STL for printing. It is a zip of XML that states its unit, so a slicer never has to guess. The converter joins vertices that sit at the same place, which turns the loose triangles of an STL into one connected mesh, and writes it as a 3MF.
An STL has no unit, and slicers read it as millimeters, so that is the starting choice here. Change it if your part was made in another unit, and the size next to the download button shows what the slicer will see. The 3MF is written in millimeters with Z up. An STL carries no colors, so none are added.
What survives the conversion
Shapes. Binary and text STL files are both read. Shapes are written as joined triangles, one object for each part.
Colors and materials. STL has no colors, so the model starts out plain. A flat color for each part is kept.
Textures. STL has no textures. Textures are not kept.
Animation. STL cannot hold animation. Animation is not kept.
Units and direction. STL does not say which unit it uses. Slicers read it as millimeters, so that is the starting choice here. The unit is millimeters, and Z points up.
If something looks wrong
If the model lies on its side, change the up direction to Y.
A model with holes or flipped faces was already broken when it was exported. Repair it with your slicer's repair tool before you print.
Joining vertices does not close holes. A mesh with gaps is still open in the 3MF.
Triangles that collapse to a line or a point once the vertices are joined are dropped.
If your slicer asks about units, the file is in millimeters.
If your browser cannot draw 3D, there is no preview, but the conversion still works.
Your file stays on your device
The converter reads your STL file in the browser and writes the 3MF file there too. Nothing is uploaded, and the page does not load anything the file points to, other than files you choose yourself. The page counts a visit like any other page, but it never sees the file's name or contents.
Questions
Is this STL to 3MF converter free, and is my file uploaded?
It is free, and you do not need an account. Your file is read and converted in your browser and never uploaded, so it stays on your device.
Why convert an STL to 3MF?
A slicer reads a 3MF without guessing its unit, and the format can hold colors and several parts. This conversion adds the unit and joins shared corners. It cannot add colors that the STL never had.
Will the 3MF hold one object or many?
One. An STL is a single mesh, so the 3MF holds a single object.
Which unit and direction does the 3MF file use?
The unit is millimeters, and Z points up.
How large a file can I convert?
Files up to 150 MB. A very large model may convert slowly on a phone or an older computer, so export only the part you need if it struggles.
More free tools
- Free 3MF to STL ConverterConvert a 3MF file to STL in your browser for printers and tools that only read STL. Free, with no upload and no sign-up.Free, in your browser
- Free STL Viewer OnlineOpen an STL file in your browser. Turn it, zoom in, and check the triangle count and size before you print. Free, with no upload and no sign-up.Free, in your browser
- Free 3MF Viewer OnlineOpen a 3MF file in your browser. Turn it, zoom in, and check the triangle count and size. Free, with no upload and no sign-up.Free, in your browser
- Free STL to GLB ConverterConvert an STL file to GLB in your browser to share a printable part on the web or in AR. Free, with no upload and no sign-up.Free, in your browser
- Free STL to OBJ ConverterConvert an STL file to OBJ in your browser to open a printable part in modeling and render apps. Free, with no upload and no sign-up.Free, in your browser
- Free 3MF to GLB ConverterConvert a 3MF file to GLB in your browser to share a printable model on the web or in AR. Free, with no upload and no sign-up.Free, in your browser
Make it a finished render
Open the studio and add your STL file. The studio opens GLB, glTF, OBJ, FBX, STL, 3MF, or DAE files. You pick the angle and describe the finish, and Inkfinish renders that view as a finished image.
Try 3 renders free, no sign-up needed: watermarked, at standard size.
Updated October 2026. Open-source licenses