How to open a .stp file
STEP 3D model · CAD / 3D
A .stp file is exactly the same as a .step file: an ISO 10303 CAD model. FreeCAD opens and edits it free, and the Windows 3D Viewer displays it without installing anything.
What a .stp file actually is
STP and STEP are two spellings of one format. The short form survives from the era when file extensions were limited to three characters, and no tool treats them differently.
If a program will not accept your .stp, renaming it to .step changes nothing about the contents and sometimes satisfies a picky file dialog.
Why it will not open
Nothing opens it by default on macOS, and on Windows the built-in 3D Viewer handles the format but is not associated with the extension, so a double-click asks what to use.
Renaming it to an extension you can open will not help: changing the extension does not convert the file, it only changes what Windows tries to open it with.
Step by step
Windows
- 01To view: right-click, choose "Open with", then 3D Viewer, included in Windows 10 and 11.
- 02To edit or measure: install FreeCAD, which is free and imports the solid geometry intact.
- 03If a program rejects the file, rename a copy from .stp to .step. It is the same data.
macOS
- 01Install FreeCAD, or "brew install --cask freecad".
- 02macOS has no built-in viewer for the format.
Programs that open .stp
Taken straight from publisher manifests. Some of these handle the format for a narrow purpose rather than as their main job.
Common questions
- Is a .stp file the same as a .step file?
- Yes, identical. Both are ISO 10303 CAD models and the shorter spelling is a leftover from three-character extension limits. Renaming between them changes nothing.
- How do I open a .stp file for free?
- FreeCAD opens and edits it on any platform at no cost. On Windows, the built-in 3D Viewer displays the model without installing anything.