Question 1

Why does the OBJ have no colour?

Accepted Answer

STL files store only triangles, so there is no colour, texture or UV data to carry over. The OBJ is written without an .mtl file and imports as plain grey geometry. Add materials in Blender after import, or UV-unwrap the mesh first if you want to paint textures.

Question 2

Why is the model on its side in Blender after STL to OBJ?

Accepted Answer

Check that “Stand upright for the new format” was on when you converted; it turns the Z-up STL into a Y-up OBJ. If you need raw coordinates, turn it off and set the axes in Blender's importer.

Question 3

What units will the OBJ use?

Accepted Answer

STL has no units, and most print files are in millimetres. At 1 : 1 scale a 50 mm part imports as 50 Blender units; use the Scale menu or Blender's import scale to change that.

Question 4

Does STL to OBJ reduce the polygon count?

Accepted Answer

No. Every triangle in the STL ends up in the OBJ; nothing is decimated, remeshed or repaired, so holes or flipped faces stay as they were. To lighten a heavy scan, add Blender's Decimate modifier after import.

Question 5

Can I convert the OBJ back to STL?

Accepted Answer

Yes, with the free OBJ to STL converter. It works the same way in your browser and turns the model Z-up again for slicers. Leave the scale at 1 : 1 both ways and the part keeps the same dimensions on the round trip.

Question 6

Is my STL uploaded?

Accepted Answer

No. The conversion happens locally with three.js inside this browser tab. The STL is never sent to a server and there is no account to create, so it suits client parts and unreleased designs under NDA.

Question 7

Can I convert STL to OBJ online for free?

Accepted Answer

Yes. The converter is free, needs no sign-in and uploads nothing, because the STL to OBJ conversion runs in your browser. You can convert up to 10 files at once, each up to 200 MB. It works in any modern browser with WebGL, on a computer or a phone, though large files are easier on a computer.

Question 8

STL vs OBJ: what is the difference?

Accepted Answer

STL is the standard 3D-printing format: a list of triangles with no colour, UVs or units, which most slicers read as millimetres. OBJ is a text format that most 3D apps and game engines import, with room for UVs and .mtl materials. Going from STL to OBJ keeps the shape but can't add what the print file never stored.

Question 9

Why does my STL to OBJ result look faceted in Blender?

Accepted Answer

STL stores every triangle on its own with a flat face normal, and the OBJ keeps them exactly that way, so curved surfaces can show facets. In Blender, select the mesh and run Merge by Distance to weld the shared vertices, then clear the custom split normals and use Shade Smooth or Shade Auto Smooth.

Question 10

Can I use the OBJ in Maya, Unity or Godot?

Accepted Answer

Yes. All three import OBJ, and an STL to OBJ conversion here already turns the mesh Y-up, the way they expect it. Mind the units: at 1 : 1 a 50 mm part becomes 50 units, and Unity and Godot treat one unit as a metre, so lower the scale in their import settings.

STL to OBJ Converter for Blender and Beyond

What the STL to OBJ converter does

How to convert STL to OBJ

Drop the STL

Convert to OBJ

Import into Blender

STL vs OBJ: what carries over

Models worth taking into Blender

Why use this STL to OBJ converter

Right way up in Blender

Keeps your numbers

Batch STL to OBJ

STL to PLY or GLB

Private

No decimation

STL to OBJ FAQ

More ways to work with your 3D files

OBJ to STL converter

GLB to OBJ converter

GLB viewer

Image to 3D

Want a model with real textures?

STL vs OBJ: what carries over	STL	OBJ
Geometry	Yes	Yes
Normals	Per face	Yes
UV coordinates	No	No
Colour, .mtl	No	No
Up axis	Z	Y