# OBJ to STL converter

> Convert OBJ models to STL (or 3MF) in your browser for 3D printing. Choose the unit the OBJ was exported in so the STL comes out the right size. Free, no upload.

Source: https://freestlviewer.com/obj-to-stl/  
Updated: October 22, 2026

Convert .obj models to STL for your slicer. Set the unit the OBJ was exported in and get a correctly sized STL — converted in your browser, never uploaded. The tool is interactive: open https://freestlviewer.com/obj-to-stl/ and drop a file onto the page.

## Why convert OBJ to STL

OBJ is common for models made in Blender, Maya, ZBrush and game pipelines,
and for downloads from 3D asset sites. Slicers read OBJ more and more, but STL
remains the format every printer workflow, print service and repair tool
accepts without question.

## The unit question

OBJ stores bare numbers. A character modelled in centimetres or a scene in
metres opens in a slicer as a tiny speck, because the slicer assumes
millimetres. Before converting, set **The file is in** to the unit the OBJ was
made in:

| Source tool or site | Usual unit |
| --- | --- |
| CAD exports, most printables | Millimetres |
| Maya, 3ds Max, many game assets | Centimetres |
| Blender default scenes, photogrammetry | Metres |
| US-based CAD set to imperial | Inches |

The summary shows the resulting size in millimetres before you download, so
you can check that a mug is 90 mm tall rather than 0.09 or 9,000.

## What is kept and what is dropped

- **Geometry:** every face, triangulated where it had four or more corners.
- **Groups and objects:** merged into one mesh in place.
- **Materials:** STL has none. 3MF output keeps the solid `Kd` colours from the
  `.mtl`.
- **Textures, UVs, normals and smoothing groups:** not used for printing and
  not written.

## Before you print

Models made for rendering are often not solid: separate floating parts, open
edges, intersecting shells. The converter's summary tells you whether the mesh
is watertight. If it is not, the slicer may still cope; if it does not, see
[watertight and manifold meshes](https://freestlviewer.com/blog/watertight-and-manifold-stl-files/).

## On a phone

OBJ conversion works in a phone browser. The Mes3D app for iPhone, iPad, Mac
and Android opens OBJ files from Files or Mail, lets you fix the unit or resize
to exact dimensions, and exports STL, OBJ or 3MF.

## Frequently asked questions

### How do I convert OBJ to STL?

Drop the .obj (or a ZIP with its .mtl and textures) onto this page, check the unit it was exported in, keep STL selected and click Convert and download. Quads and polygons are triangulated and the STL is written in millimetres.

### Why is my converted STL tiny or huge?

OBJ has no unit. Files from animation and game tools are often in centimetres or metres, which a slicer reads as millimetres. Pick the right source unit before converting and the STL comes out at real size.

### Are materials and textures kept?

Not in STL, which stores geometry only. Choose 3MF to keep the solid colours from the .mtl; image textures are not carried over by either format.

### Does OBJ to STL lose detail?

No. The triangles are written exactly as they are; quads and n-gons are split into triangles, which is how slicers would treat them anyway.