What is a .step file?
STEP / ISO 10303 CAD Model · 3D model · ISO · 1994
STEP is the neutral, standardised format for exchanging precise 3D CAD models between different engineering programs. It stores exact solid geometry rather than a triangle mesh, which makes it the interoperability backbone of manufacturing and product design.
What is a .step file used for?
Defined by the ISO 10303 standard, a STEP file stores true solid geometry (a precise boundary representation), so the model stays exact and editable rather than being flattened into triangles like an STL.
Its whole purpose is interchange: a part designed in SolidWorks, Fusion 360, CATIA or FreeCAD can be handed to any of the others as a .step or .stp and keep its precision.
The file is ASCII text beginning with ISO-10303-21;, so you can even open it in a text editor, though you need CAD software to work with the geometry.
For 3D printing or rendering, a STEP is usually converted to a mesh format like STL or OBJ.
How to open a .step file
The .step format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- FreeCAD
- Fusion 360
- SolidWorks
- online CAD viewers
macOS
- FreeCAD
- Fusion 360
- online CAD viewers
Linux
- FreeCAD
- online CAD viewers
Web
- Online CAD / STEP viewers
How to convert a .step file
You can convert a .step file to STL, OBJ, IGES using a conversion tool or the export menu of an app that opens it.
.step file signature (magic bytes)
Programs recognise a .step file by the bytes at the start of the file, not by its name. These are the signatures for STEP.
| Hex signature | Offset | Note |
|---|---|---|
| 49 53 4F 2D 31 30 33 30 33 2D 32 31 | 0 | 'ISO-10303-21;' header (ASCII STEP) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .step file?
STEP is the neutral, standardised format for exchanging precise 3D CAD models between different engineering programs. It stores exact solid geometry rather than a triangle mesh, which makes it the interoperability backbone of manufacturing and product design.
How do I open a STEP or STP file?
Use CAD software such as the free FreeCAD, Autodesk Fusion 360, or an online CAD viewer. .step and .stp are the same format under two names.
What is the difference between STEP and STL?
STEP stores exact, editable solid geometry for engineering, while STL stores a fixed triangle mesh for 3D printing. Convert STEP to STL when you are ready to print; go the other way is much harder, since a mesh has lost the precise geometry.
Related formats
Sources
Details on this page were checked against authoritative references: