STEP (.stp CAD)
Also known as: .step file, .stp file, ISO 10303, how to open STEP
STEP (.step or .stp) is an open, international-standard format for sharing precise 3D CAD models between programs. Unlike a triangle mesh, it stores exact solid and surface geometry, making it the common neutral format for mechanical and product design.
- Open ISO-standard 3D CAD exchange format (.step/.stp)
- Stores exact solid geometry, not a triangle mesh
- The default neutral format for mechanical design
What a STEP file stores
STEP is defined by the ISO 10303 standard and is not tied to any one vendor, which is why it is the default way to exchange engineering models. It uses the .step or .stp extension and stores its data as text.
Crucially, STEP keeps exact geometry — the mathematical curves and solid bodies (B-rep) of a part — rather than approximating it with triangles like STL or OBJ. That precision is what lets another CAD program reopen the model and keep working on it.
How to open and use STEP
Mechanical CAD tools — Fusion 360, SolidWorks, FreeCAD, Onshape, and many others — import and export STEP, so it is the file you send when a collaborator uses different software. Free CAD viewers and online viewers open it for inspection.
When a part needs to be 3D printed instead of edited, the STEP model is exported to a mesh format like STL. For pure 2D drawings, DWG and DXF remain the relevant formats.