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How to convert OBJ to STL

You may not need to: most slicers open OBJ. How to convert OBJ to STL in Blender, check it, and when to choose 3MF instead.

Aman PorwalFounder @ Vi3W

3 min read

A pencil sketch of a brass lantern on paper, with the same lantern rising off the page as a solid, lit object

Quick answer

How do you convert OBJ to STL?

Often you don't need to: most slicers, including PrusaSlicer and Bambu Studio, open OBJ directly and slice it. To convert anyway, import the OBJ into Blender, apply transforms, check the mesh, and use File › Export › STL. Or open it in a slicer and export STL from there. Colour and textures are lost, because STL stores only geometry.

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First: do you need to convert?

STL became the default for 3D printing, but it isn't the only format printers' software accepts. PrusaSlicer's documentation lists STL, STEP, 3MF, OBJ and AMF as supported formats. Bambu Studio and Cura also open OBJ. If your slicer opens the OBJ and it slices cleanly, you can skip conversion.

Convert when a print service, a website or older software asks for STL specifically.

OBJ vs STL in one line each

Converting OBJ to STL throws away the UVs and materials. For single-colour printing, nothing is lost that matters.

Method 1: Blender (free, most control)

  1. File › Import › Wavefront (.obj).
  2. Check size in the sidebar (N) under Dimensions. Blender's metric units are metres; slicers usually read STL numbers as millimetres. If you want a 100 mm model, either set it to 0.1 m and export with the right scale, or set Unit Scale so 1 unit = 1 mm. Scaling for printing covers this properly.
  3. Select the object and Ctrl+A › All Transforms.
  4. Optional but recommended: run the free 3D Print Toolbox extension's checks for non-manifold edges and thin walls. Make a model watertight.
  5. File › Export › STL (.stl). Tick Selection Only if the scene has other objects. Choose Binary for smaller files (ASCII is readable but much bigger).

Method 2: your slicer

  1. Open the OBJ in PrusaSlicer, Bambu Studio, Cura or similar.
  2. Let it repair any reported errors.
  3. Use the slicer's export option to save as STL (in PrusaSlicer: File › Export › Export Plate as STL).

Fast, though you get less control over repair than in Blender.

Method 3: online converters

Plenty exist. Fine for quick, non-sensitive files. Check the file size limit, and don't upload anything confidential.

Common problems

  • Model is tiny or huge in the slicer: units. STL has none; set scale in the slicer or Blender.
  • Slicer reports errors: non-manifold geometry or holes. Repair in the slicer or Blender.
  • Lost colours: expected. For colour, use 3MF instead; see multicolour prints from AI models.
  • Several objects in one file: export them together or separately as needed.
  • Inside-out faces: recalculate normals in Blender (Edit Mode › Mesh › Normals › Recalculate Outside).

For AI-generated models

Vi3W exports OBJ (geometry only), GLB and FBX, but not STL. OBJ is the natural choice for printing: open it in the slicer, or convert it with the steps above. Generated models also benefit from a quick watertight check before slicing. The AI 3D printing workflow covers the full route from generation to print.

Got a model idea? Generate it in Vi3W, export OBJ, and slice it as-is or convert in Blender.

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