My sample is pen-cup.glb, a small test model I made for this post. It is a pen cup authored in metres, 0.08 × 0.09 × 0.08 m, Y-up as glTF expects. It has two meshes (a hollow wall and a base disc) under a parent node that moves them away from the origin, and one terracotta-coloured material.

What a GLB to STL conversion keeps and drops

• Geometry stays. The visible mesh surfaces are written as triangles.
• Everything else is dropped. STL has no materials, textures, vertex colours, animation or hierarchy. The terracotta colour will not survive.
• Placement can be baked in. With Apply transforms on, node position and scale go into the coordinates.
• Separate meshes become shells. The wall and base end up in one STL as separate shells.
• No repair. Open surfaces stay open; the converter doesn't add wall thickness or close gaps.

Step 1: Open the converter and set the options first

Go to the GLB to STL converter on 3dconverter.org. The page shows a drop zone, a summary of what is kept in the STL and what is left out, and a settings panel. The file is processed in your browser; the page says there is no model upload.

The converter before a file is chosen: drop zone, "Kept in the STL / Left out" summary and the settings panel.

One thing to know before you start: the converter runs as soon as you choose a file, and there is no separate Convert button. The settings can only be changed before a file is loaded, so set them now:

• Unit: auto, mm, cm, m or inch. Set it explicitly; millimetres are the usual choice for slicers.
• Up axis: auto, y-up or z-up. glTF is Y-up.
• Apply transforms: bakes node placement and scale into the coordinates. Keep it on so the parts stay where the scene put them.
• Recalculate normals: recomputes face normals. I left it off.
• STL encoding: binary or ascii. Binary is smaller and is what most slicers expect.

For the pen cup I chose mm, left the up axis on auto, kept Apply transforms on, left Recalculate normals off and picked binary. Until a file is chosen, the button at the bottom of the panel just reads "Choose a file first".

Settings before loading: Unit = mm, up axis auto, Apply transforms on, Recalculate normals off, binary encoding.

Step 2: Choose the GLB

Click Choose a GLB file or drop the file onto the page. The page accepts single-file binary glTF (.glb), up to 20 files at once, and it offers a sample ("Glazed mug GLB") if you don't have a model handy.

Conversion starts immediately. A moment later the page shows "Converted", a split preview of the source and the output, and a Download STL button.

After conversion: split preview of the GLB source and the STL output, with the Download STL button and the size table.

The table next to the preview compares the source (in m) with the STL (in mm). For the sample it reads:

• X × Y × Z: 0.08 × 0.09 × 0.08 m in the source, 80 × 90 × 80 mm in the STL.
• Triangles: 768 in, 768 out.
• Materials: 1 in the source, 0 in the STL.

That is the same physical cup: converting metres to millimetres multiplies every coordinate by 1,000 but keeps the real size.

Step 3: Read the full quality report

Below the preview, expand Full quality report. It reopens the STL and checks it against the source, one card per feature.

The expanded quality report: geometry kept, warnings for materials and hierarchy, units changed from m to mm, axis kept as Y-up.

For the pen cup:

• Geometry is preserved (768 → 768 triangles).
• Materials and Hierarchy are flagged, because STL can't keep them.
• Units changed from m to mm.
• Axis was kept as Y-up.
• The report also notes that the output was parsed again successfully.

A good readback only means the STL could be parsed and matched the source. It doesn't prove the model is watertight, has printable wall thickness or fits your build plate.

Step 4: Download and check it before slicing

Click Download STL and keep the original GLB next to it. The GLB remains your source for colour, materials and scene structure; an STL can't give them back.

Then open the STL in a viewer or your slicer:

1. Measure a known dimension. The cup should be 80 mm wide. If it shows as 0.08 mm or 80 m, the unit was misread.
2. Check the orientation. The cup should stand upright. If it lies on its side, re-run with the other up-axis option rather than rotating by eye.
3. Count the shells. The wall and base are separate shells here. Many slicers handle this, but a repair tool may want them merged.
4. Run the slicer's checks. Look at manifold state, wall thickness and supports with the printer and material you will actually use.

Left: the converter's split preview of source and output. Right: the downloaded STL in a viewer, upright, 768 triangles.

Common questions

Why is my converted STL tiny or huge? glTF uses metres. If the unit is left to a guess and the slicer reads millimetres, a 0.08 m cup becomes 0.08 mm. Choose the unit before loading the file and check the reported size.

I loaded the file and forgot to set the unit. Now what? Settings can only be changed before a file is loaded, so set the unit first, then choose the file. If you missed it, use the Change file button to start again.

Will the STL keep my textures? No. If appearance matters, keep the GLB, or convert to a format that can carry more of the source, such as OBJ.

Does conversion make a model printable? No. Thin parts and open surfaces can look perfect in a web viewer and still fail as a solid. Treat the STL as the start of print preparation.

Recap: set unit, up axis and encoding → choose the GLB (it converts automatically) → read the size and quality report → download → measure and check in your slicer.

Disclosure: I make 3D Converter, the browser tool used in this walkthrough.

I'm using a small sample model: a 0.5 m textured wooden crate (wooden-crate.glb, one material with a base color texture).

What survives the trip (and what doesn't)

OBJ is a much simpler format than GLB, so it helps to know the limits up front:

• Kept: geometry. Materials, textures, units, axis convention and multiple objects are kept partially: each material keeps its base color, opacity and base color texture, written to an MTL file.
• Left out: vertex colors, animation, skins, scene hierarchy, cameras, lights and metadata. Metalness, roughness, normal and emissive maps have no MTL equivalent.

In other words, the OBJ is a static, editable copy of the geometry with simple textured materials. Keep the GLB as your source of truth.

Step 1 — Open the GLB to OBJ converter

Open the GLB to OBJ converter on 3dconverter.org. Free local conversions don't need an account or sign-up.

The converter page: drop zone on the left, output panel on the right, and the "Kept / Left out" summary for this route.

Step 2 — Add your GLB file

Click Choose a GLB file or drag the .glb onto the drop zone. The page processes the file in a Web Worker in your browser tab — the model is not uploaded to a conversion server. You get an interactive preview (drag to rotate) and a compatibility report for the GLB → OBJ route.

The sample crate loaded locally, with a rotatable preview and the converter's output panel. The "Kept / Left out" summary above shows what OBJ can and cannot carry.

Note that the page only reads the file you select; it does not fetch anything a model references from a web address.

Step 3 — Choose units, up axis and transforms

Open Settings before converting. glTF uses meters and Y-up, while OBJ applications vary, so this route lets you make both explicit:

• Unit: auto, mm, cm, m or inch. Converting meters to millimeters scales coordinates by 1,000.
• Up axis: auto, Y-up or Z-up. Changing it rotates the geometry.
• Apply transforms: bakes node position, rotation and scale into the mesh so the OBJ matches the visible static pose.
• Recalculate normals: optional.

Pick the destination unit and up axis first. Write both choices down with the asset.

If your GLB is animated, pause on the pose you actually want first. The converter exports static geometry and does not keep a rig or animation clips.

Step 4 — Convert and read the validation report

Run the conversion. When it finishes, the browser reopens the new OBJ with the matching loader and compares it with your GLB: dimensions, object count, triangle count, materials and textures. Rows the OBJ cannot represent — hierarchy and animation — show a warning instead of a match.

Triangles, size (X × Y × Z) and unit, before and after. For the crate, the 12 triangles and the 0.5 m size should match.

Be clear about what this check proves: it catches empty or unreadable output. It does not repair a mesh, certify printability, or make the two formats lossless.

Step 5 — Download the OBJ package

When the GLB has materials, the download is a ZIP containing the .obj, the .mtl and the original base color images, copied unchanged. Texture coordinates are flipped to the OBJ convention for you.

Keep the OBJ, MTL and image files together in one folder — the OBJ references the MTL, and the MTL references the texture.

Step 6 — Check the result in your target app

Open the OBJ in the editor you plan to use and run four quick checks:

1. Pose: it's the static pose you wanted (animation can't come back later).
2. Scale and orientation: compare the dimensions and up axis with the settings you chose, instead of trusting import defaults.
3. Parts: object and triangle counts look right, even though the original scene tree is gone.
4. Materials: base colors and textures appear; expect PBR details (metalness, roughness, normal maps) to be missing.

Before (GLB) and after (OBJ): same shape and base texture, with the static pose baked in.

When not to use OBJ

Don't use OBJ as an archive for a complete GLB scene. If you need the full PBR material set, rigging, animation clips, cameras or lights to stay editable, open the GLB in a glTF-aware authoring tool and export a fuller package there. For simple shape work, a textured preview or a legacy OBJ pipeline, a browser-side GLB → OBJ conversion with a before-and-after report is quick and keeps the model on your machine.

Quick recap: open the converter → add the GLB → set unit, up axis and transforms → convert and read the report → download the ZIP (OBJ + MTL + textures) → check scale, pose and materials in your editor.

Disclosure: I make 3D Converter, the browser tool used in this walkthrough.