STEP (ISO 10303) .step
The ISO standard for CAD exchange. Real solids, not triangles.
What an .step file holds
STEP is how serious CAD data moves between systems that share no code. It describes a part as a boundary representation, trimmed analytic and NURBS surfaces stitched into watertight solids, carrying tolerances and assembly structure rather than a mesh. Converting it means tessellating those surfaces into triangles, and that is a one-way trip: exact geometry is replaced by an approximation of it, and the parametric history is gone.
Commonly seen in: SolidWorks, CATIA, Fusion 360, Siemens NX, Creo, FreeCAD, Onshape.
| Data | Stored in STEP |
|---|---|
| Geometry | Yes |
| Materials and colour | Yes |
| Texture maps | No |
| Animation and rigs | No |
| Scene hierarchy | Yes |
| Read here | Yes |
| Written here | No |
Tested against a real file
The last sweep loaded rounded-cube.step from occt-import-js test files through the viewer on this site: 84 triangles across 1 meshes and 1 materials, in 3.5 seconds. Every format's result is on the test results page, run 2026-09-08.
Which way is up
STEP is a Z-up format, which most of the rest of 3D is not. Files are read exactly as written and stood up for you in the viewer; the converter has a switch for it, so a model does not arrive in the next program lying on its side.
Convert STEP to another format
Every pairing has a page saying what survives the trip.
Other things to do with an .step file
Questions about STEP
How do I open an .step file?
Drop it into the viewer on this site and it opens in the browser, with the scene tree, the materials and the mesh statistics. Nothing is uploaded. If you want it in another program instead, convert it to GLB, which almost everything reads.
Is STEP a good format to archive in?
STEP stores geometry, materials and colour, scene hierarchy. Anything outside that list will not be in the file at all, so archive the original alongside it if the surfacing or the rig matters.
Does converting STEP lose quality?
Geometry is copied vertex for vertex, so the shape does not degrade. What gets lost is whatever the target format has no field for: convert to STL and the materials go, convert to OBJ and the animation goes. The comparison table on each converter page says exactly which.
Written up on the blog
Formats that hold the same things
Or go back to the full format reference.