Can this convert a file into GLB and then back out again?

Not yet — GLB (binary glTF) is currently export-only here. You can convert an STL, OBJ, or PLY file into a GLB, but not the other direction.

Does this preserve materials, textures, or colors?

No — this covers geometry only (positions and triangle indices). The source formats parsed here don't carry material or texture information either, so there's nothing to preserve on that front.

Will I keep my colours and textures?

No. Only vertex positions and triangle connections are kept. Colours, textures, material files, UV coordinates and source normals are ignored, and the OBJ, PLY, GLB and 3MF outputs carry none of them. STL files contain face normals worked out from the triangles.

Why does my model come out the wrong size?

GLB assumes metres and 3MF assumes millimetres, while STL, OBJ and PLY have no unit. Set Model units to what the source used before converting, and the tool scales to metres for GLB or millimetres for 3MF. For the other targets the setting is not applied to the coordinates.

What does the Reduce triangles slider do?

It removes triangles by merging the least important edges first, aiming for the percentage of the original count that you chose, down to 5 percent. A note after conversion shows the before and after counts. Lower values mean smaller files with less detail, so inspect the result.

What does the watertight check mean?

After duplicate vertices are merged, the tool counts the faces that meet at each edge. If every edge joins exactly two faces, the mesh is reported watertight and volume and surface area are shown. Otherwise you see the open-edge count and any edges shared by three or more faces. Nothing is repaired unless you tick "Fill small holes", which closes small open loops when you convert and re-checks the result.

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3D Mesh Converter (STL/OBJ/PLY/GLB/3MF)

Convert between STL, OBJ, PLY (ASCII or binary), GLB and 3MF, with size and 3D-printing checks

Files never storedRuns on your device

Drop an STL, OBJ, PLY, GLB or 3MF fileTap to choose an STL, OBJ, PLY, GLB or 3MF file

or click to browseor tap to choose

Convert between 3D mesh formats — runs entirely in your browser

Large files (over 50 MB) may take longer or run out of browser memory

About 3D Mesh Converter (STL/OBJ/PLY/GLB/3MF)

Converts 3D mesh files between STL, OBJ, PLY (ASCII and binary), GLB (glTF) and 3MF, entirely in your browser. It merges duplicate vertices (so OBJ/PLY/GLB files are much smaller), writes face normals for STL output (OBJ, PLY and GLB are written without them), and checks the model (size, watertight, volume) before you download. You can tick "Fill small holes" to close open loops in a model that is not watertight, and scale the exported model by a factor or to a target size. A slider can also reduce the triangle count (mesh simplification) for big scans.

Watch: 3D Mesh Converter (STL/OBJ/PLY/GLB/3MF) in Action

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Can this convert a file into GLB and then back out again?: Not yet — GLB (binary glTF) is currently export-only here. You can convert an STL, OBJ, or PLY file into a GLB, but not the other direction.
Does this preserve materials, textures, or colors?: No — this covers geometry only (positions and triangle indices). The source formats parsed here don't carry material or texture information either, so there's nothing to preserve on that front.
Which formats can it read and write?: It reads STL (ASCII or binary), OBJ, PLY (ASCII or binary, either byte order), GLB and 3MF. It writes STL binary, STL ASCII, OBJ, PLY binary, PLY ASCII, GLB and 3MF. The format is detected from the file extension, and a loose .gltf file is not accepted.
Will I keep my colours and textures?: No. Only vertex positions and triangle connections are kept. Colours, textures, material files, UV coordinates and source normals are ignored, and the OBJ, PLY, GLB and 3MF outputs carry none of them. STL files contain face normals worked out from the triangles.
Why does my model come out the wrong size?: GLB assumes metres and 3MF assumes millimetres, while STL, OBJ and PLY have no unit. Set Model units to what the source used before converting, and the tool scales to metres for GLB or millimetres for 3MF. For the other targets the setting is not applied to the coordinates.
What does the Reduce triangles slider do?: It removes triangles by merging the least important edges first, aiming for the percentage of the original count that you chose, down to 5 percent. A note after conversion shows the before and after counts. Lower values mean smaller files with less detail, so inspect the result.
What does the watertight check mean?: After duplicate vertices are merged, the tool counts the faces that meet at each edge. If every edge joins exactly two faces, the mesh is reported watertight and volume and surface area are shown. Otherwise you see the open-edge count and any edges shared by three or more faces. Nothing is repaired unless you tick "Fill small holes", which closes small open loops when you convert and re-checks the result.

How to use 3D Mesh Converter (STL/OBJ/PLY/GLB/3MF)

Drop an STL, OBJ, PLY, GLB or 3MF file; the format is read from the extension. Choose Convert to from seven options: STL binary, STL ASCII, OBJ, PLY binary, PLY ASCII, GLB or 3MF. Set Model units (millimetres, centimetres, metres or inches), which matters mostly for GLB and 3MF output because those are rescaled to metres and millimetres. If you like, lower the Reduce triangles slider, which runs from 100 percent down to 5 percent in steps of 5.

Press Convert. A report shows vertex and triangle counts, the bounding box and whether the mesh is watertight, and then you can download. When the units are millimetres you can also enter your print bed size to see whether the part fits.

When to use it

Use it when a slicer, game engine or viewer rejects the format you have: an OBJ that must become a binary STL for printing, an STL you want as a compact GLB for a web page, or a 3MF that a simpler program cannot open. It is also useful for thinning a heavy scan with the triangle slider and for a quick watertight check before printing.

When not to use it

Do not use it when colours, textures, materials, UV maps, animations or rigging must survive, because only geometry is carried across. For CAD sources such as STEP or IGES, or for editing and repairing a mesh, you need a modelling program such as Blender or a CAD package. It also will not fix holes it reports; it only tells you they exist.

Tips for best results

Check Model units before you press Convert. STL, OBJ and PLY carry no unit, so that setting is what lets a GLB come out in metres and a 3MF in millimetres at the right size. For a big scan, try keeping half the triangles first and compare the counts in the note beneath the report. Choose binary STL or binary PLY for smaller files, and the ASCII versions only if you want to read them in a text editor.

Limitations

Only triangle positions survive. Colours, textures, materials, UVs, normals and scene hierarchy are dropped, and OBJ, PLY and GLB outputs carry no normals, so viewers work out their own shading. Everything in a GLB or 3MF is merged into one object. GLB input must be a self-contained .glb; separate .gltf files are not accepted, and Draco-compressed files may fail. Simplification trades detail for size, and zero-area triangles are removed.

Privacy

The model is read and rewritten inside the page, so the file is not uploaded. GLB reading uses a three.js loader, and 3MF files are unpacked with a zip library; both are loaded on demand from this site's own scripts, and neither sends your geometry anywhere. The converted file exists only in your browser until you download it.