Why people convert STL to OBJ
STL is the file slicers read. OBJ is plain text with vertices, faces and optional texture coordinates, and modeling programs import it readily. It is the usual way to take a printed part into a scene, paint it, unwrap it for textures or render a product shot.
The converter does one job here. It rewrites the triangles of your STL as OBJ faces, and everything you add afterwards (materials, UV maps, lighting) happens in the program you open it with.
What the STL to OBJ conversion carries over
| Property | Result |
|---|---|
| Triangles | Copied one to one; the count in Info matches before and after |
| Size | Same numbers: a 20 mm cube is 20 units wide in the OBJ |
| Quads | Not created; an STL has only triangles to give |
| Color, materials, UV | None, because the STL had none |
Wanted clean quads for sculpting or subdivision? That needs retopology in a modeling program. A file converter cannot guess the original quad layout from triangles.
Convert STL to OBJ online, step by step
- Press Open File or drop the .stl on the drop zone. Binary and ASCII STL both open.
- Wait for the bar that reads
name.objwith its size. - Orbit the model, or use Section to look inside, if you want to check it first.
- Open Info and note the triangle count, so you can compare it after import.
- Press Download OBJ. Convert another file starts over with the next STL.
Large STL files and what slows them down
There is no file-size cap; the memory of the tab is the limit. In tests a 12 MB STL with 250,000 triangles opened in about 1.5 s. A 48 MB STL with a million triangles took 5 to 12 s and about 1.2 to 1.7 GB of memory.
A binary STL takes 84 bytes plus 50 bytes per triangle, so a 100 MB file holds about two million triangles. That sits at the edge where the tab may run out of memory. For a heavy scan, simplify the STL first: a test sphere reduced to 30 % of its triangles kept its volume within 2 %.
Problems after you import the OBJ
- The part is 1,000 times too big or too small. The OBJ carries the STL's millimeter numbers, and your scene may count in meters. Scale it on import, or use Edit → Size here before converting.
- Shading looks faceted. STL stores flat triangles with one normal each. Smooth shading is a setting in the modeling program, not something the file can carry.
- Dark patches on the surface. Some triangles face inward. Edit → Repair makes normals consistent and outward; convert again afterwards.
Tested result and where to go next
A 20 mm cube and a test sphere were converted from STL to OBJ, opened again and compared: size, volume and triangle count matched. Your file is read and written by code running in this tab, and in the full test run no request went to another domain.
To check the result, open it in the OBJ viewer. Need it back for printing? OBJ to STL does the reverse. For a slicer that wants a project file, use STL to 3MF; for CAD, STL to STEP builds a faceted solid.
Questions and answers
Can you convert STL to OBJ without losing quality?
Yes. Every triangle is copied as it is, and the test compares size, volume and triangle count after re-opening the OBJ.
Can the OBJ have quads instead of triangles?
No. The STL only holds triangles, so the OBJ does too. Quads come from retopology in a modeling program.
Is there a limit for STL files over 100 MB?
No fixed limit. A million triangles (48 MB) opens in 5 to 12 s; above roughly 1 to 2 million triangles the tab may run out of memory.
Do I need Python or a script to convert STL to OBJ?
No. The conversion runs in the browser tab with nothing to install. Drop the file, then press Download OBJ.
Will the OBJ come with an .mtl file or color?
An STL carries no color or material, so there is nothing to put into one. You add materials in the program that opens the OBJ.
Will the OBJ be bigger than my STL?
Usually, because OBJ is plain text and binary STL is not. If size matters, reduce triangles in Edit before converting.
Can I paint the OBJ for a render after converting?
Yes. Open the OBJ in your modeling program, unwrap it for UV coordinates and assign a material there. The converter gives you the clean triangle shape to start from; the paint job, lighting and camera are set up afterwards in that program.