# OBJ to STL Converter

> Get OBJ models from Blender, ZBrush or an AI generator ready for your slicer: every face kept, quads split into triangles, standing up on the plate at a sensible size.

Page: https://printpal.io/convert/obj-to-stl
Updated: 2026-11-12
Use it: open https://printpal.io/convert/obj-to-stl in a browser and drop a file. Free, no account, files are processed locally and never uploaded.

OBJ is what Blender, ZBrush and AI generators hand you; STL is what every slicer and print service expects. OBJ to STL keeps every face, splits quads and n-gons into triangles, and drops what STL can't hold: materials, textures, UVs and vertex colors.

OBJ has no units, so its numbers pass straight through as millimetres. If the model was built in metres (a Blender character 1.8 units tall would print 1.8 mm tall), the preview flags it and offers to read the file as metres. OBJ is also Y up by convention, so the converter stands it upright for the slicer's Z up; switch the up axis if your OBJ was already Z up.

## How to convert OBJ to STL

1. **Drop your OBJ files.** Drop the .obj with its .mtl and texture images, or a .zip of the folder.
2. **Check the preview.** The model appears at the size and orientation it will have. Fix the file units, up axis or size under Size, units and orientation if needed.
3. **Choose STL options.** Binary STL by default (smallest, read everywhere). Tick ASCII only if an old tool asks for text STL.
4. **Convert and download.** One file downloads straight away. A batch gives a download per file and one .zip of all of them.

## What carries over

| | Result |
|---|---|
| Geometry | Every face is kept; quads and n-gons are split into triangles. |
| Color | Dropped: STL cannot store color. |
| Units | OBJ has bare numbers, so they pass through as millimetres: 1 unit becomes 1 millimetre. If the preview size is wrong, set the file units. |
| Orientation | Turned from Y up to Z up, so it stands on the plate in a slicer. |
| Objects | Merged into one surface: STL has no objects. |

## OBJ at a glance (Wavefront OBJ)

OBJ came out of Wavefront Technologies' animation software and became the plain-text lingua franca of 3D. The geometry is in the .obj; colors and texture references live in a companion .mtl file, which is why OBJs so often arrive grey.

- **Stores:** Vertices, faces (triangles, quads, n-gons), UVs and normals as text
- **Color:** Materials and textures in a separate .mtl file; vertex colors as an unofficial extension
- **Units:** None, the numbers are bare
- **Up axis:** Y by convention (Blender, Maya, most 3D apps)
- **File size:** Text: about a binary STL's size for bare geometry, up to twice that with UVs and normals
- **Opens in:** Blender, Maya, 3ds Max, ZBrush, Cinema 4D, game engines, most slicers

## STL at a glance (Stereolithography (Standard Triangle Language))

Created by 3D Systems in 1987 for the first stereolithography printers, STL is still the format every slicer and print service accepts. It describes a surface as a list of independent triangles, with no shared vertices, units, colors or scene structure.

- **Stores:** Loose triangles: three corners and a normal each, binary or ASCII
- **Color:** None in the standard
- **Units:** None written; slicers assume millimetres
- **Up axis:** Z, the slicer convention
- **File size:** 50 bytes per triangle in binary, about 5 times that as ASCII
- **Opens in:** Every slicer, CAD tool and 3D app

## Tips

- **Skip the .mtl** STL drops colors anyway, so the .obj alone is enough.
- **Check it's watertight** Sculpts and scans often have holes. Open the STL in the [STL viewer](https://printpal.io/tools/stl-viewer) for a mesh check, and fix it in [Mesh Repair](https://printpal.io/tools/mesh-repair) if needed.
- **Keep the colors** Printing in several colors? Convert [OBJ to 3MF](https://printpal.io/convert/obj-to-3mf) instead: material colors become filaments.

## FAQ

### Why is my STL tiny or huge after converting from OBJ?

OBJ stores numbers without units. A model built in metres reads as millimetres and comes out tiny. Set the file units to metres in the converter (it suggests this when the size looks wrong), or scale it in your slicer.

### Does OBJ to STL keep textures?

No. STL stores geometry only. Use 3MF for filament colors, or keep the OBJ or GLB for textured renders.

### My OBJ has quads. Is that a problem?

No. Quads and n-gons are split into triangles, which is what STL stores and what a slicer works with anyway.

### Is the converter free? Are there limits?

Free, with no sign-up, watermark or file count limit. Batches and files of a few hundred MB work on most laptops; the only limit is your device's memory.

### Are my files uploaded?

No. Files are read and written by JavaScript and WebAssembly in your browser and never sent to PrintPal. The STEP and IGES reader is the only extra download, once, from a public CDN.

## Related

- [STL to OBJ Converter](https://printpal.io/convert/stl-to-obj)
- [STL to 3MF Converter](https://printpal.io/convert/stl-to-3mf)
- [STL to GLB Converter](https://printpal.io/convert/stl-to-glb)
- [OBJ to GLB Converter](https://printpal.io/convert/obj-to-glb)
- [STL to PLY Converter](https://printpal.io/convert/stl-to-ply)
- [OBJ to 3MF Converter](https://printpal.io/convert/obj-to-3mf)
- [STL to USDZ Converter](https://printpal.io/convert/stl-to-usdz)
- [OBJ to USDZ Converter](https://printpal.io/convert/obj-to-usdz)
- [3D model viewer](https://printpal.io/tools/3d-model-viewer)
- [3D model converter](https://printpal.io/tools/3d-model-converter)
- [Mesh Repair](https://printpal.io/tools/mesh-repair)
- PrintPal for LLMs: https://printpal.io/llms.txt