STL ⇄ OBJ 3D Model Converter
Convert STL, OBJ, PLY, 3MF, AMF, GLB — batch, with unit fix.
More free tools
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, game and 3D-editing software only accepts one of them. This tool does a real conversion: it parses the triangle and vertex data from your file and rebuilds it in the target format — binary or ASCII STL, OBJ, binary or ASCII PLY, 3MF, AMF, OFF or GLB. Drop in several files at once and you get a list of results with one-click downloads and a ZIP of everything.
Unit and axis options solve the problems that usually follow a conversion: choose the source units (or let the file's own unit be used) and the output units to convert inches to millimetres in the same step, rotate Y-up game assets to Z-up for printing, apply an extra scale factor, and move the part to the print bed. A 3D preview with volume, size and a watertight check lets you verify the result before it reaches your slicer.
Use it in 4 steps
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.
Key features
Eight output formats
STL (binary/ASCII), OBJ, PLY, 3MF, AMF, OFF and GLB from any supported input.
Batch + ZIP
Convert many files at once and download them together.
Units, axes, scale
Inch/mm/cm/m conversion, Y-up → Z-up and extra scale in the same step.
Preview & check
3D preview with size, volume and watertight status.
A real example, step by step
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.
Frequently asked questions
Can I convert many files at once?
Yes — drop several files; each is converted and you can download them individually or as a ZIP.
Does it keep colours and textures?
No — only the mesh geometry is converted; STL cannot store colours and OBJ materials are not carried over.
Can it convert CAD STEP files?
Use the STEP to STL converter; STL to STEP is available too.
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.
Free, fast and private by design
No signup, no watermark. New AZRS tools are added every week.
