# STL to OBJ converter

The STL to OBJ converter reads a binary or ASCII STL in your browser and writes an OBJ with a plain gray MTL, zipped together. STL carries no unit, so it is read in millimetres unless you choose centimetres, metres or inches, and the OBJ is written Y-up in metres for 3D apps.

> Canonical: https://ai3d.studio/stl-to-obj

## STL to OBJ in numbers

### 4 units to read the STL in

Millimetres by default, or centimetres, metres or inches when the STL was drawn in one of those.

### 1,000 mm per OBJ unit

A part 50 mm tall in the STL is 0.05 units tall in the OBJ, which a program reading OBJ in metres shows as 50 mm.

### 0 UVs, 0 textures

An STL stores triangles alone, so the OBJ has no texture coordinates and one plain gray material.

### 250 MB per file

The largest STL the page opens; it is read inside the browser tab and 0 bytes are uploaded.

## The sample fox through the STL to OBJ converter

Read back from the downloaded ZIP.

### 247 KB of STL in, 205 KB of ZIP out

The binary STL fox, 5,054 triangles, became a ZIP holding a 1.99 MB OBJ and a 69-byte MTL; the OBJ is text, so it unzips to about eight times the STL.

### Z height became Y height

Read in millimetres, the fox stood 998 mm tall on the STL's Z axis; the OBJ gives the same 0.998 m to its Y axis, so it stays upright in a Y-up program.

### No texture coordinates written

The OBJ holds 15,162 vertices and normals and no vt lines, because the STL had no UV layout to pass on.

## What survives STL to OBJ

An STL has little to lose; most rows are about what it never held.

### Every triangle

Kept

### Flat shading

Kept

### Surface

Added

### Scale and up axis

Changed

## Why an STL needs a unit before it becomes an OBJ

The same numbers mean different sizes to a slicer and to a modeling program.

### An STL's numbers have no unit

The file stores bare coordinates. Slicers read them as millimetres, which is the convention the converter starts from.

### OBJ readers tend to think in metres

Blender, Unity and Godot take one OBJ unit as a metre, so the converter divides millimetres by 1,000 to keep the real size.

### Printers stand parts on Z, OBJ on Y

An STL is Z-up for the print bed, while OBJ files are conventionally Y-up and importers such as Blender's convert from that; turning the part keeps it standing.

## Convert an STL to OBJ in three actions

The page opens with OBJ picked; the unit is the one choice worth a look.

### Drop the STL

Pick the .stl, binary or ASCII. The page names the format, counts the triangles and shows the size in millimetres.

### Check the unit

If the size reads 25.4 times too small, the STL was drawn in inches; 10 times too small, in centimetres. Pick that unit.

### Convert and unzip

Press Convert to OBJ and unzip the download, keeping the .obj and .mtl side by side.

## Limits of STL to OBJ conversion

The OBJ cannot hold more than the STL had to give.

### No texture to recover

The OBJ is bare shape without a UV layout. AI retexture with TRELLIS.2 takes the STL or the OBJ and paints a new textured surface.

### A wrong unit guess changes the size

An inch STL read as millimetres comes out 25.4 times too small. The size readout shows it before you convert.

### Facets stay facets

Nothing is smoothed, so a coarse print mesh looks just as coarse in a renderer; a remesh or a polygon pass comes after.

## Where an STL goes next

The return trip, the print formats and ways to give the bare shape a surface.

### [OBJ to STL](https://ai3d.studio/obj-to-stl)

The opposite direction, with the unit chosen before the STL is written.

### [STL to 3MF](https://ai3d.studio/stl-to-3mf)

Keep the part printable with its millimetre unit written into the file.

### [STL viewer](https://ai3d.studio/stl-viewer)

Look at the part from every side before converting it.

### [AI retexture](https://ai3d.studio/ai-retexture)

TRELLIS.2 Retexture takes an STL or OBJ and returns a textured GLB.

### [Every 3D conversion](https://ai3d.studio/3d-file-converter)

All formats the converter reads and writes, from GLB to USDZ.

## Questions about STL to OBJ

Answers about size, orientation, color and privacy.

### How do I convert an STL to OBJ?

Drop the .stl on the converter, check that the size readout looks right, and press Convert to OBJ. A ZIP downloads with the OBJ and its MTL.

### What size is the OBJ after STL to OBJ conversion?

The same physical size. A part 50 mm tall in the STL is 0.05 OBJ units tall, which is 50 mm in a program that reads OBJ in metres; pick inches or centimetres first if the STL was drawn in those.

### Why does the model stand differently after STL to OBJ?

STL parts stand on Z for the print bed, while OBJ files are conventionally Y-up and importers such as Blender's convert from Y-up. The converter turns the part so it arrives upright.

### Does STL to OBJ add color or textures?

No. An STL holds triangles only, so the OBJ gets one plain gray material and no UV layout. AI retexture with TRELLIS.2 can paint a surface onto the STL or the OBJ afterwards.

### Who uses STL to OBJ, and for what?

People bringing a printable part, a 3D scan or a downloaded model into Blender, a renderer or a game engine to texture, render or remix it. For printing, the STL itself or a 3MF is the better file.

### Is STL to OBJ conversion free and private?

Yes. The STL is read and the OBJ is written in your browser tab, with no account, no credits and 0 bytes uploaded.

### Can I use what STL to OBJ makes commercially?

Every plan, the free tier included, lets you use what STL to OBJ makes commercially: the outputs generated for you are yours.

### How does STL to OBJ compare, and what alternatives fit a different workflow?

STL to OBJ: Convert STL to OBJ free in your browser: binary or ASCII STL in, an OBJ and MTL out, stood Y-up and scaled from millimetres to metres. Nothing is uploaded. Related options are AI 3D model editor: AI 3D model editor for a mesh you already have: upload GLB, OBJ, FBX or STL up to 200 MB, then retexture, remesh, rig or segment it. From 25 credits a tool, FBX to STL: Convert FBX to STL free in your browser: centimetres become millimetres, the model turns Z-up for the slicer, and you can set a print height of 28 to 180 mm, FBX to OBJ: Convert FBX to OBJ free in your browser: the OBJ, its MTL and the FBX's color textures as PNG files come in one ZIP, in metres. Nothing is uploaded, GLB Compressor: Free GLB compressor: meshopt or Draco geometry, WebP, JPEG or PNG textures resized to 512–4096 px, optional simplification. Runs in your browser, no upload, OBJ to STL: Convert OBJ to STL free in your browser: an OBJ has no unit, so you set one; the part is turned Z-up and written in millimetres. Nothing is uploaded, and 3D Turntable Video: Free 3D turntable video maker: spin a GLB, FBX, OBJ or STL through 360° and download a looping MP4 or a transparent WebM, up to 4K and 60 fps. Choose by the required input, delivered output, controls, limits, current availability, and credit cost; the related-tools section links each canonical page.

## Convert an STL to OBJ now

Drop the .stl above and save the OBJ.

## Related tools

### [AI 3D model editor](https://ai3d.studio/ai-3d-model-editor)

### [FBX to STL](https://ai3d.studio/fbx-to-stl)

### [FBX to OBJ](https://ai3d.studio/fbx-to-obj)

### [GLB Compressor](https://ai3d.studio/glb-compressor)

### [OBJ to STL](https://ai3d.studio/obj-to-stl)

### [3D Turntable Video](https://ai3d.studio/3d-turntable-video)

_Last updated October 8, 2026_