OBJ to STL: Which File to Use, and How to Convert
OBJ, STL and GLB all describe a 3D shape, but they keep different things. Picking the right one saves you a conversion, and knowing the traps of converting saves you a failed print. Here's what each format is for, and how to turn an OBJ into an STL when you really need to.
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Free preview, no account. Pay €1 only for the model you keep: OBJ, STL and GLB in one download.
Or open an example model
OBJ vs STL vs GLB at a glance
| OBJ | STL | GLB | |
|---|---|---|---|
| Shape (mesh) | Yes | Yes, triangles only | Yes |
| Colour / texture | Yes, via separate .mtl and image files | No | Yes, inside the file |
| Units | None | None (slicers assume mm) | Metres |
| Files | 2–3 that must stay together | 1 | 1 |
| Best for | Blender, Maya, Unity, general 3D tools | 3D printing, CAD | Web, AR, Unreal, Blender |
If your model came from OBJify, skip the conversion
Every OBJify download is a ZIP with all three formats. The STL isn't just the OBJ saved differently: it's a separate, cleaned copy that has been made watertight, set to millimetres and stood flat on the build plate, so it slices without repairs.
| File in the ZIP | What it is | Use it for |
|---|---|---|
model.glb |
Mesh, colour texture and material in one file. Y-up, about 1 m on its longest side. | Blender, Unreal, Unity (with glTFast), websites, AR |
model.obj + material.mtl + texture image |
Textured mesh, about 1 unit on its longest side, stored Z-up. Keep the three files in the same folder. | Unity, Maya, Cinema 4D, any 3D tool |
model_3dprint_150mm.stl |
Watertight solid, no colour, in millimetres: 150 mm on its longest side, standing on Z = 0. | Slicers, Fusion 360, FreeCAD |
Models are around 55,000–60,000 triangles with a single colour texture (no normal or roughness maps). Files are deleted from our servers after an hour, so keep the ZIP.
Do you need STL at all?
Probably less often than you think. Bambu Studio, OrcaSlicer, PrusaSlicer and Cura all open OBJ files directly. You need an STL when:
- a print service or marketplace only accepts STL;
- a CAD tool (like Fusion 360 or FreeCAD) or an older tool wants it;
- you want a single file without the .mtl and texture images hanging around.
Convert OBJ to STL in Blender (free)
- File → Import → Wavefront (.obj) and choose the OBJ.
- Check the size in the side panel (N → Dimensions). Your slicer will read 1 Blender unit as 1 mm, so scale it to the print size in millimetres and apply the scale (Ctrl+A → Scale).
- File → Export → STL (.stl), tick Selection Only if there are other objects in the scene, and save.
More Blender tips are in the Blender guide.
Convert OBJ to STL in PrusaSlicer (free)
- Drag the OBJ onto the plate. If it looks tiny or huge, set its size in the object panel.
- If the model shows a warning sign, right-click it and use the repair option.
- File → Export → Export Plate as STL.
Three things that go wrong
- Wrong size. OBJ has no units, so a model built in metres turns into a 1 mm speck, and one built in millimetres can fill the room in a game engine. Always check the dimensions after converting.
- Holes and thin walls. Meshes made for screens don't have to be closed, but prints do. Slicers can fix small problems (Fix model in Bambu Studio's right-click menu, the repair option in PrusaSlicer). Bigger gaps need repair in Blender or Meshmixer.
- Lying on its side. Different tools use different up axes. If the model comes in on its back, rotate it in the slicer or use Lay on face before slicing.
What about 3MF?
3MF is a newer format made for 3D printing. Unlike STL, it records units and can carry colour and print settings, and it's the native project format of Bambu Studio and PrusaSlicer. If your tools support it, exporting 3MF avoids the size guesswork entirely.
Frequently asked questions
What is the difference between OBJ and STL?+
Both store a 3D shape as a mesh. OBJ can also store texture coordinates and point to a material and texture images, so it keeps colour. STL stores only triangles: no colour, no materials and no units. Slicers assume STL units are millimetres.
Do I need to convert OBJ to STL for 3D printing?+
Often not. Most slicers, including Bambu Studio, OrcaSlicer, PrusaSlicer and Cura, open OBJ files directly. Convert when a tool or print service only accepts STL. OBJify downloads already include a print-ready STL, so you can skip conversion entirely.
How do I convert OBJ to STL for free?+
In Blender, import the OBJ and use File, Export, STL. In PrusaSlicer, import the OBJ and use File, Export, Export Plate as STL. Both are free. Check the size afterwards, because OBJ files have no units.
Why is my converted STL tiny or huge in the slicer?+
OBJ has no units, so the same numbers can mean metres, centimetres or millimetres. Slicers read STL numbers as millimetres. A model that was 1 unit tall becomes 1 mm. Scale it in the slicer or before exporting.
Why does my converted STL have errors in the slicer?+
Meshes made for screens often have holes or thin walls, which is fine for rendering but not for printing. Slicers can repair simple problems: right-click the model and choose Fix model in Bambu Studio, or use the repair option in PrusaSlicer. OBJify's STL is already made watertight.
Which format should I use: OBJ, STL, GLB or 3MF?+
STL or 3MF for 3D printing and CAD, GLB for the web, AR and game engines that support glTF, and OBJ when a 3D tool needs a textured mesh it can open everywhere. 3MF is a newer print format that can also store units and colour.
Try it with your own photo
Free preview, no account. Pay €1 only for the model you keep: OBJ, STL and GLB in one download.
Or open an example model