Free 3D Model Converter

Vertex color preservation across formats:

• GLB / glTF — full support (COLOR_0 attribute). Native.
• PLY — full support, used heavily in scanning workflows.
• FBX — supported but inconsistent across versions / exporters. Some FBX consumers ignore vertex colors.
• OBJ — limited support. Standard OBJ doesn't have vertex colors; some extensions add them but most importers ignore.
• STL — no support. Geometry only.
• 3MF — supports per-face/vertex colors and is the right print-format choice when colors must survive.

When converting from GLB:

• Printer with color support (Bambu AMS, Prusa MMU): export 3MF directly from Meshy.
• Renderer / engine: keep GLB. Don't convert to OBJ.
• Research/scanning workflow: PLY.
• FBX-only destination: convert via Blender, verify vertex color export setting in the FBX export dialog.

Meshy exports GLB, FBX, OBJ, USDZ, STL, 3MF directly from the same task — pick the format that keeps the data your destination needs.

Unit consistency depends on explicit unit handling at conversion time. Reliable approaches:

1. Meshy's export — download multiple formats from the same task. All come from the same internal mesh, so scale and orientation match across GLB/OBJ/STL.
2. Blender — File → Import, then Scene Properties → Units → Length: Millimeters or Meters. Re-export with consistent units across formats. Reliable for batch work via scripting.
3. gltf-transform CLI — preserves units of source GLB; doesn't re-scale. Good for GLB → optimized GLB.
4. Assimp library — programmatic conversion with unit awareness; good for custom pipelines.

Avoid converters that don't expose unit settings — they often default to "as-is" which leads to silent unit drift.

Standard practice: Pick mm or meters as your project default. Ensure every export step uses that unit. Re-import to validate; bounding-box dimensions should match expectations. STL is unitless — apply your unit convention consistently when slicing or scaling.

Free options:

1. Blender — $0 desktop app, imports/exports virtually any 3D format, scriptable; learning curve is real.
2. Online converters (Online-Convert, FreeFileConvert) — $0, web-based, basic STL/OBJ/GLB conversions, file-size limits.
3. Microsoft 3D Builder — $0, basic mesh repair + format conversion (STL/OBJ/3MF).
4. gltf-transform CLI — $0, scriptable for GLB optimization and format swaps.

Paid converters / pipelines:

1. Meshy — Free tier (limited credits) → ~$20/mo Pro. Not just a converter — generates models from text/image, multi-format export (GLB, FBX, OBJ, STL, USDZ, BLEND, 3MF), Remesh, AI Texturing, Animate. ROI is in generation + conversion combined.
2. Spin 3D Mesh Converter — ~$30 one-time, 50+ formats, batch conversion.
3. Polygon Cruncher — ~$200, mesh optimization + conversion.
4. RapidPipeline (DGG) — enterprise, automated optimization + format conversion at scale.

What paid tiers deliver over free:

• Batch processing
• Higher file-size limits
• PBR material preservation across format swaps
• Automated optimization (decimation, Draco compression)
• Commercial-use licenses and API access

For pure conversion of <100 files/year, Blender + gltf-transform CLI is enough. For scale, automation, or generation alongside conversion, Meshy's Pro tier replaces 3–4 separate tools.

GLB → OBJ with consistent scale and orientation:

1. Cleanest path — re-export from Meshy. The same task that produced the GLB also exports OBJ; both come from the same internal mesh, so scale and orientation match.
2. If you only have the GLB, use Blender:
   • File → Import → glTF 2.0 (.glb / .gltf). Confirm the model loads at the expected scale.
   • File → Export → Wavefront (.obj). In the export dialog, set Forward = -Z and Up = Y to match GLB conventions. Set Scale = 1.
   • This preserves scale and the GLB's Y-up coordinate system in the OBJ.
3. Watch for unit conversions — Blender works in meters; OBJ has no unit metadata. Verify scale post-import in your target program.
4. Materials — OBJ + MTL doesn't carry PBR. Textures will export, but the metalness/roughness won't survive. For PBR fidelity, stay in GLB.

For batch conversions, command-line tools like gltf-pipeline + custom scripts work, but the Blender path is most reliable for one-offs.