Turn OBJ models into STL files for your slicer. Convert up to 200 files at once; MTL files and textures in the same drop are matched automatically.
Drop OBJ files hereRelease to convert
or
OBJ, MTL, textures, a folder or a ZIP · up to 200 files
No file at hand?
Drop more OBJ files hereRelease to convert
OBJ, MTL, textures or a ZIP · up to 200 files
Click a file to preview it.
Preview
Settings
Binary is smaller and opened by every slicer. ASCII is human-readable.
OBJ stores no units. Pick what the model was made in so the print comes out the right size.
Merges corners that almost touch, closing hairline gaps so slicers see one solid.
How it works
Choose your OBJ files
Drop files, a folder or a ZIP. They are read by your browser and never sent anywhere.
Check the preview
See the size in mm, the triangle count and whether the mesh is watertight before you print.
Download the STL
One file at a time, or all of them as a single ZIP.
Settings explained
STL encoding
Binary STL stores each triangle in 50 bytes after an 84-byte header, and every slicer and CAD program reads it. ASCII STL writes the same triangles as text, which makes the file about four times larger (3.8 times for a 1-million-triangle test model).
Choose ASCII only if you want to read, search or compare the file as text. The shape is the same either way.
OBJ units
Neither OBJ nor STL records units: the files hold plain numbers. Slicers read STL numbers as millimetres, so the converter multiplies by the unit you pick: centimetres by 10, metres by 1 000 and inches by 25.4.
Most CAD programs export millimetres. Blender works in metres by default, so a part modelled 0.05 units wide becomes 50 mm with Metres. If a converted part shows up 10, 1 000 or 25.4 times too small in the slicer, it was made in centimetres, metres or inches.
Weld duplicate vertices
STL stores every triangle with its own three corners. After an export, corners that should be the same point sometimes differ in the last decimal, which leaves hairline gaps that slicers report as holes or non-manifold edges.
With Weld on, corners closer than 1/100 000 of the model’s bounding-box diagonal (about 0.002 mm on a 100 mm cube) are moved onto one point, and triangles that collapse to a line are removed. With Weld off, every triangle is written exactly as it was read.
OBJ vs STL
OBJ stores each corner once, faces with any number of corners, and colours and textures through an MTL file. That suits modelling programs and game engines. STL stores only triangles, each with its own three corners, which is all a slicer needs.
Converting to STL splits every face into triangles and drops materials and object names. The shape is kept: STL stores coordinates as 32-bit floats, the precision slicers work with.
| Property | OBJ | STL |
|---|---|---|
| Full name | Wavefront Object | Stereolithography (also read as Standard Triangle Language) |
| Extension | .obj (+ .mtl for materials) | .stl |
| MIME type | model/obj | model/stl |
| Encoding | Text | Binary or text (ASCII) |
| Surface | Polygons with any number of corners | Triangles only |
| Shared vertices | Yes | No, every triangle stores its own corners |
| Colours and materials | Yes, in a separate MTL file with texture images | No, not in the standard |
| Units | Not stored | Not stored |
| Several objects | Yes, named objects and groups | No, one list of triangles |
| Opened by | Modelling programs (Blender, 3ds Max, Maya), game engines and most slicers | Every slicer and CAD program |
FAQ
My OBJ has an MTL file and textures. Do I add them?
You can drop them together, or in one ZIP, and they are matched to the OBJ automatically. STL cannot store colour, so only the shape is kept, and the file list says what was dropped. For a multi-colour print, paint the model in your slicer after converting.
Why is my model the wrong size in the slicer?
OBJ has no units, and slicers read STL as millimetres. Set OBJ units to what the model was made in and every file is converted again: centimetres are multiplied by 10, metres by 1 000 and inches by 25.4. Blender’s default unit is the metre.
Does an OBJ with several objects become several STL files?
No. All objects and groups are merged into one STL at their own positions, since STL has no way to keep them apart. The file list says how many were merged.
What happens to quads and other polygons?
Faces with four or more corners are split into triangles fanning out from their first corner, as every OBJ importer does. That is exact for flat, convex faces. Triangulate concave faces in your modelling program before you export.
How large can the files be?
Files are converted in the background, so the page stays responsive. A 1-million-triangle OBJ of 26 MB converts and shows its preview in about three seconds on a laptop. Phones have less memory; if a file is too large for the device, the file list says so instead of failing silently. Up to 200 files can be converted at once.
How can I check that nothing is uploaded?
Open your browser’s developer tools, go to the Network tab and convert a file. You will see no request carrying your file. Once the page has loaded, converting works without an internet connection.