STEP File Format (.stp)

An STP file holds a STEP product model in ISO 10303's plain-text exchange syntax, encoding exact boundary-representation solids, surfaces and curves rather than a triangulated mesh.

.stp3D Models

STEP at a glance#

Full name	ISO 10303 STEP
File extension	.stp
Category	3D Models
Developer	ISO Technical Committee 184, Subcommittee 4
First released	1994
MIME types	model/stepmodel/step+xmlmodel/step+zip
Other extensions	.step
Compression	Lossless
Specification	ISO 10303-21 (STEP Clear Text Encoding)
FileFlip support	FileFlip writes this format but cannot open one

What a .stp file can hold#

These are the things a STEP file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Embedded metadata	Yes
Comments	Yes
Schema or validation	Yes

Strengths and limitations of STEP#

What STEP does well

Carries exact boundary-representation geometry, NURBS surfaces and precise curves, rather than an approximated mesh, so dimensions stay exact
Vendor-neutral: essentially every mechanical CAD system past and present can read and write it
Application Protocols like AP242 standardise how tolerances, PMI and assembly structure travel alongside the geometry

Where STEP falls short

The same feature can come out differently depending on which Application Protocol, and which CAD system, wrote the file
Large assemblies produce very large, verbose text files
No tessellated mesh is included by default, so anything expecting triangles has to tessellate the boundary representation first

Use STEP whenever exact CAD geometry, not an approximated mesh, needs to move between two different CAD systems.

Convert a STEP file to a mesh format like STL or OBJ once the model is finished and only needs to be viewed, rendered or 3D printed rather than edited as a solid.

How to open a .stp file#

A .stp file opens in the programs below, grouped by the platform you are on.

Platform	Programs that open it
Windows	SolidWorks, Autodesk Fusion, Siemens NX, CATIA, FreeCAD
macOS	Autodesk Fusion, FreeCAD
Linux	FreeCAD

STEP questions people ask#

What does STP stand for?

STP is the file extension for STEP, the Standard for the Exchange of Product model data, formally ISO 10303. It's the neutral format mechanical CAD systems use to hand solid models to each other.

What's the difference between STP and STEP files?

None functionally; .stp and .step are the same STEP exchange format under different extensions, both readable by any application that supports one or the other.

Why do STEP files use exact curves instead of triangles?

STEP stores boundary-representation geometry, meaning surfaces are defined by exact mathematical definitions like NURBS rather than approximated with flat triangles the way STL does. That's what lets a STEP file be reopened in another CAD system and edited as a true solid, not just viewed.

Can I 3D print a STEP file directly?

Most slicers can't read STEP directly, since it describes exact surfaces rather than the triangle mesh a slicer expects. Converting to STL or 3MF tessellates the STEP model's boundary representation into triangles first.

Converting STEP files#

FileFlip cannot open a .stp file, so there is nothing to convert it into here. It appears on the site as something other formats can be converted to.

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.