How to convert a STEP file to GLB

Convert a STEP CAD file to a small GLB for the web, on your own computer and for free. The model is never uploaded. Drop it in, check it, export.

A STEP file is how engineers share a design. A web page cannot show one. GLB is the format it can show: a compact 3D file that browsers, AR viewers and most 3D programs open. This page takes you from one to the other with MeshOptimiser, on your own computer. Nothing is uploaded, and there is nothing to pay.

What you need

MeshOptimiser, started once. See What you need and Start it the first time.
Your model as a STEP file (.step or .stp). If it is still in your CAD program, see Native CAD files: export a STEP file first.

Steps

Start the app with start.bat (Windows) or start.command (macOS).
Drag the STEP file onto the window.
In the Import settings window, leave everything as it is and press Import. Tessellation quality at Standard (0.5) is the recommended choice. See Open your first file.
Wait while the progress card works. A big assembly can take several minutes. Repeated parts are found and stored once, and the result is compressed.
Look at the model. Properties on the right shows how heavy it is. Press 1 for the normal view.
Press CtrlE and choose GLB. In the Export window, check Unit scale and Up axis (below).
Press Export GLB. The file arrives in your downloads folder.

Two settings that save a second try

Unit scale: CAD models are usually in millimetres, and glTF and most web viewers expect metres. If the model shows up a thousand times too big in the viewer, export again with × 0.001 (mm → m).
Up axis: CAD uses Z as up. glTF uses Y. If the model lies on its back in the viewer, export with Y-up (glTF, OBJ, Maya).

Leave Draco compression off unless the viewer you use can read it. See Which format should I choose.

How small will it be?

It depends on the model. The app’s README gives one example: a 320 MB STEP file became an 11 MB compressed GLB. Assemblies with many identical parts, such as bolts, shrink the most, because each shape is stored once. That is an example, not a promise for every file.

If the GLB is still too heavy, remove what nobody will see before you export. A sensible order to work in shows how, and Fit to budget takes a triangle count for the whole scene.

Without opening the viewer

To convert a file and do nothing else, drag it onto step2glb.bat (Windows) or step2glb.command (macOS). The GLB is written next to it. Or use the command line:

python step2glb.py input.step --meshopt

The command line is described in The command-line converter. Meshopt compression needs the free tool gltfpack on your PATH. If a viewer cannot open a Meshopt-compressed GLB, convert again with --no-meshopt, or export from the app instead.

To see what the conversion did, read How to read the numbers. For the file formats in detail, see Export.