SliceLoft

OBJ to STL Converter

Turn an OBJ model into STL, preview its shape and check the size before you print.

Files stay in your browser. No upload. No sign-up.

Drop OBJ or ZIP files here or click to choose

Open one or more OBJ files, with optional companion MTL and texture files, or include them together in a ZIP. Up to 300 MB total; 1,000,000 triangles. Materials and textures are used for preview only.

Try an OBJ model before choosing your own files.

OBJ does not reliably identify the model’s physical units. Millimeters are selected by default. Choose the units used to create the model and check the dimensions before downloading.

Mouse: drag to rotate, scroll to zoom, Shift + drag to pan.Touch: drag to rotate, pinch to zoom, two-finger drag to pan.

Choose an OBJ or ZIP file to begin.

How to convert OBJ to STL

  1. Open your model. Drop an .obj file into the box, or choose a ZIP containing the OBJ and any companion MTL and texture files.
  2. Check size and orientation. Preview the model, choose its source units and check the dimensions in millimeters. Leave Y-up to Z-up enabled for a Y-up source, or turn it off if the model already uses Z-up.
  3. Download your STL. Combine the loaded objects into one STL, or download a ZIP with one STL per object. Binary STL is the default; choose ASCII if your workflow requires it. Open the result in your slicer and check the slicing preview before printing.

OBJ vs STL: what is the difference?

OBJ can describe a polygon mesh with object or group names, texture coordinates and references to materials. Its companion MTL file can describe materials and point to texture images. Keep those files together when you want the original appearance to display. See the Blender OBJ documentation.

STL describes a surface as triangles. The STL exported here contains geometry only, with no colors, textures or material assignments. STL also has no unit field, so checking the intended size matters even after conversion. See the three.js STL exporter documentation.

Use OBJ to STL conversion when your next tool or print service asks for STL, or when you want geometry-only files for individual objects. Keep the original OBJ, MTL and textures if you will need the model’s appearance later.

Check units and Y-up orientation before exporting

Choose the source units. The default is millimeters. If the model was created in centimeters, meters or inches, choose that unit so the coordinates are converted to millimeter-sized output: 1 cm becomes 10 mm, 1 m becomes 1,000 mm, and 1 inch becomes 25.4 mm. This is a unit conversion, not automatic size detection. The exported STL still has no unit field; import it as millimeters and check the dimensions in your slicer.

Check which direction is up. Some OBJ workflows use Y as the vertical axis, while 3D-printing workflows commonly use Z. The Y-up to Z-up switch rotates a Y-up model into Z-up orientation and is on by default. Turn it off for a model already exported as Z-up. This changes orientation, not scale, and does not choose the best printing angle or add supports. Axis conventions depend on the source exporter; see the Blender OBJ axis settings.

Frequently asked questions

Is my OBJ or ZIP uploaded to a server?

No. Reading the model, converting the mesh and packaging the download happen locally in your browser. Conversion runs in a Web Worker on your device. Your OBJ, MTL, textures and ZIP contents are not uploaded for conversion, and no account is required. Feedback you choose to submit is sent separately from conversion.

Will the STL keep colors, materials and textures?

No. Companion MTL and texture files are used for preview only. The exported STL contains triangle geometry and does not preserve colors, textures or material assignments. Keep the original files if you need that information later. Separate STL files also need any filament assignments to be set again in your slicer.

Can I use the STL in Bambu Studio, PrusaSlicer or Cura?

Yes. These slicers support STL model import. Open the downloaded STL as a model, check its size and orientation, then choose your printer, filament and print settings. A successful import does not guarantee a successful print. These slicers also support OBJ, so conversion may be unnecessary if your original file already works for your workflow. See the PrusaSlicer file-format guide for its supported formats.

Why is my model tiny or too large after conversion?

A source-unit mismatch is a common cause. For example, a model that is 2 inches wide becomes only 2 mm wide if its coordinates are treated as millimeters. Choose Inches as the source unit to make that width 50.8 mm. Check a known dimension instead of guessing from the preview. The Y-up to Z-up switch changes orientation only; it does not fix scale.

Can I open a ZIP and export objects separately?

Yes. You can open a ZIP containing an OBJ and its companion MTL and texture files. Keep the file names and relative folder structure unchanged so the preview can resolve the references. To export, combine the loaded objects into one STL or download a ZIP with one STL per object. Combining objects places their triangles in one file; it does not perform a boolean union or repair overlapping geometry.

Does OBJ to STL conversion automatically repair the model?

No. The tool reports degenerate triangles, open edges and non-manifold edges without repairing the mesh. You can try the repair tools available in your slicer, then inspect the result and slicing preview before printing. Some models need editing in a modeling application. See Prusa’s repair guidance.

Need to inspect the result? Open it in the STL Viewer. To package an STL as a basic 3MF model, use STL to 3MF. For an existing 3MF model, use 3MF to STL.