Convert OBJ to STL
Convert OBJ to STL in your browser. The conversion runs on this page and the file never leaves your computer.
Result
Before you convert: what this keeps and what it destroys
Preserved
- The geometry, triangle for triangle
- Overall dimensions and proportions
- Watertightness, where the input is watertight
Destroyed
- A recorded unit: STL stores none
- Colour
- The separation between parts, merged into one body
↺ the reverse: STL → OBJ · about .obj · about .stl · just view it instead
Why people convert OBJ to STL
Usually you downloaded a model from a 3D asset site, where OBJ is common, and your slicer wants STL.
OBJ keeps object and group names, and STL has nowhere to put them, so a multi-part model merges into one body. OBJ's colours live in a separate .mtl file, which is discarded, though if you only uploaded the .obj they were never there to begin with.
Neither format has a unit, so nothing is scaled and nothing is guessed. If the model was made for a game engine it may be in metres or in arbitrary units, and it will arrive in your slicer either microscopic or enormous. Check the dimensions.
What you get
You get a binary STL file containing the same triangles the OBJ file described. No geometry is added, removed or approximated: mesh-to-mesh conversion is a change of container, and this site's tests check that the triangle count comes out identical.
Not carried across by this conversion: a recorded unit, colour, the assembly structure.
The conversion runs in your browser. Your file stays on your computer and is not uploaded.
What to check afterwards
- OBJ carries no unit. The numbers in the file are just numbers, so the conversion assumes millimetres. Check the overall dimensions of the result before you commit to machining or printing it. A file exported from a package set to inches will be 25.4 times out.
- Colour is lost. STL has nowhere to store it. If colour matters, pick a target that keeps it: 3MF, GLB, PLY or USDZ.
- Separate parts merge into one body. OBJ can describe an assembly and STL cannot, so a multi-part model arrives as a single mesh. 3MF and GLB both keep the structure if you need it.
- Coordinates are stored as 32-bit floats. For a part measured in millimetres that's far finer than any machine tolerance. For a model spanning hundreds of thousands of units it isn't.
If you need something this conversion cannot give you
If the unit has to be unambiguous, convert to 3MF instead. It records the unit in the file, so nobody downstream has to assume millimetres and nobody has to scale by 25.4 after the fact.
If colour has to survive, convert to 3MF for printing, GLB for the web, or PLY if the colour is per-vertex scan data.
If the parts must stay separate, convert to 3MF or GLB. Both keep a real structure, so a five-part assembly arrives as five parts rather than one merged body.
If your slicer accepts 3MF, consider it when you need a unit declaration or separate components in the output. Keep the original project for its print settings.
Going the other way
Convert STL back to OBJ. The reverse conversion also works with mesh geometry. It does not reconstruct exact CAD surfaces. Material data and part structure lost in either direction cannot be restored by converting back. Keep the original file for later edits.
How we know this conversion works
This pair was checked against 3 files from the test corpus on 2026-09-04. Each run parses its own output back in and compares the bounding box, the triangle count and, for closed solids, the volume against the input.
A pair that fails those checks doesn't get a page. That's why this site lists 120 conversions and not the several hundred a format-times-format grid would suggest.