STL ⇄ OBJ 3D Model Converter
Really convert between STL and OBJ, plus a unit-scale option · free, no signup
See STL ⇄ OBJ 3D Model Converter in action
Free STL ⇄ OBJ 3D Model Converter
STL and OBJ are both triangle-mesh formats, but a lot of CAD, slicer and 3D-printing software only accepts one or the other. This tool does a real conversion: it parses the real triangle and vertex data from your uploaded file (STL in binary or ASCII, or an OBJ with v/f face data) and rebuilds it in the target format, choosing binary STL, ASCII STL or OBJ as the output.
An optional scale factor lets you convert units at the same time — for example multiplying by 25.4 to turn an inch-based model into millimetres (the unit nearly every slicer expects), or dividing by 25.4 to go the other way. The converted mesh is rendered so you can confirm it looks right before downloading.
Key features
Real mesh conversion
Parses the actual triangle/vertex data and rebuilds it in the target format — not a renamed file.
Both directions
STL to OBJ or OBJ to STL, with binary or ASCII STL output.
Optional unit scale
Multiply every coordinate by a scale factor, handy for inch-to-mm conversion before slicing.
Preview before download
Renders the converted mesh so you can check it before saving.
How to use it
- Drop in an .stl or .obj file.
- Choose the output format (binary STL, ASCII STL or OBJ).
- Optionally set a scale factor for unit conversion.
- Preview the result and click Download.
Worked example
Example
An OBJ model exported in inches converts to STL with a 25.4 scale factor applied, producing a millimetre-scale STL ready to load directly into a slicer.
Who uses this tool
Makers whose slicer only accepts STL
Convert an OBJ export from a 3D design tool into STL in one step.
Anyone importing a printed model into a 3D editor
Convert STL to OBJ for tools that expect OBJ's vertex/face format.
People fixing a model exported in the wrong units
Apply a real scale factor during conversion instead of rescaling manually in a separate program.
Tips for the best results
- OBJ files can reference vertex normals and texture coordinates the model doesn't need for 3D printing — this converter reads the vertex/face geometry (the part that matters for STL) and doesn't preserve textures.
- If a slicer reports a model is the wrong size by close to a factor of 25.4, the source file was very likely modeled in inches — use the scale factor to fix it in the same step as the format conversion.
- Binary STL produces a much smaller file than ASCII STL for the same mesh — prefer binary unless a specific tool requires ASCII.
Common mistakes to avoid
- Assuming format conversion alone fixes a differently-scaled model — if the original units were wrong, apply the matching scale factor during conversion rather than guessing dimensions later in a slicer.
- Expecting OBJ texture/material data to carry over — this conversion preserves the real geometry (vertices and faces), which is what matters for 3D printing, not textures or materials.
- Converting a non-manifold or otherwise broken mesh and expecting the converted file to suddenly be watertight — format conversion doesn't repair mesh geometry issues.
Why use AZRS QuickFix?
It is 100% free, needs no signup and has no watermark or usage limits. The tool runs in your browser, so what you type stays on your device, and it works on phones, tablets and desktops. New tools are added every week — bookmark this page or browse the full QuickFix toolbox.
Frequently asked questions
Does this actually convert the file, or just rename it?
It genuinely parses the real triangle/vertex data and rebuilds the file in the target format — STL and OBJ store geometry differently, so a rename alone would not work.
Can I convert OBJ to STL and back without losing precision?
Coordinates are carried through as full floating-point values, so there's no meaningful precision loss from the format conversion itself.
What does the scale factor do?
It multiplies every vertex coordinate by the number you enter — use 25.4 to convert inches to millimetres, or 1/25.4 (≈0.03937) to convert millimetres to inches.
Does it preserve color or texture data?
No — it preserves the mesh geometry (vertices and faces), which is what 3D printing and most CAD/slicer workflows need; OBJ material/texture references are not carried over.
Is my file uploaded anywhere?
No. Parsing, conversion and rendering happen entirely in your browser; the file is never sent to a server.