What is a STEP file?

A STEP file (.step or .stp) is a 3D CAD model saved in the ISO 10303 standard, the neutral format every major CAD program can read and write. Unlike a mesh, it stores the exact geometry of each part: true planes, cylinders and curved surfaces, with their edges, plus the unit and the structure of an assembly.

Drop your STEP file here

Extensions	.step, .stp
Name	Standard for the Exchange of Product model data
Standard	ISO 10303-21
Stores	Exact surfaces and solids (B-rep), assemblies
Colour	Per body or face, in AP214 and AP242
Units	Stored in the file
Opens in	FreeCAD, Fusion, SolidWorks, Onshape, Inventor, this page

Why engineers send STEP files

Every CAD program has its own native format: SLDPRT for SolidWorks, F3D for Fusion, IPT for Inventor. None of them opens the others reliably. STEP is the format they all agree on, so it is what a supplier, a machinist or a client sends when they do not know which CAD tool you use.

Because it keeps exact geometry, a STEP file is good enough to machine from. A hole is still a cylinder with a diameter, not a ring of flat triangles that approximates one.

AP203, AP214 and AP242

STEP is a family of application protocols, and the export dialog in your CAD tool may ask which one to use. AP203 is the original for mechanical parts and stores shape only. AP214 came from the car industry and adds colours and layers. AP242 merges both and adds product data such as dimensions and tolerances. When in doubt, choose AP214 or AP242.

How to open a STEP file without CAD software

The viewer at the top of this page opens STEP and IGES files in your browser, using OpenCascade, the same open-source geometry kernel as FreeCAD. Nothing is uploaded. For more than viewing:

FreeCAD is free and opens STEP natively, with measuring and editing.
Fusion has a free personal-use licence.
Onshape has a free plan and runs in a browser, but public plans make your documents public.
PrusaSlicer and Bambu Studio import STEP directly for printing.

STEP to STL for 3D printing

Most slicers want triangles, so a STEP file has to be converted to STL first. The conversion cuts every curve into small flat faces. The finer the cut, the smoother the print and the larger the file. The STEP to STL converter does this in your browser, in millimetres, ready for a slicer. Keep the STEP file: it is the exact master, and you cannot get the exact surfaces back from an STL.

Free tools for STEP files

STEP viewer Open a STEP or IGES CAD file without CAD software. STEP to STL Turn a STEP file from CAD into an STL for your slicer. 3D file viewer Open any common 3D file in your browser.

Frequently asked

What is the difference between .step and .stp?

None. They are the same format. The three-letter .stp extension dates from systems that allowed only three characters. Rename one to the other and every program reads it the same way.

Is a STEP file the same as an STL?

No. A STEP file stores exact surfaces and solids, with units and assembly structure, and can be edited in CAD. An STL stores only flat triangles that approximate the surface, with no unit. You can turn STEP into STL easily, but not back again with the exact geometry.

Can I open a STEP file in Blender?

Not out of the box. Blender works with meshes, and STEP is not a mesh. Convert the STEP to STL or OBJ first, or use a Blender add-on that imports CAD files.

What is an IGES file?

IGES (.iges, .igs) is the older CAD exchange format, from 1980. It stores surfaces but handles solids less reliably than STEP, and is mostly found in older workflows. The viewer on this page opens IGES files too.