STEP (.step or .stp) and IGES (.iges or .igs) are the files engineers send each other when they don't use the same CAD program: SolidWorks, Fusion 360, Inventor, CATIA, Creo, NX, Onshape and FreeCAD all export them. Opening one usually means installing a CAD program or a vendor's viewer, and the 3D printing and design tools most people have - Windows 3D Viewer, Blender, slicers - can't read them at all, because a STEP file describes exact curved surfaces rather than triangles.
This page reads the model with OpenCascade, the open-source CAD kernel behind FreeCAD, compiled to run in your browser. It works out the surfaces, draws the model with its colours and edges, and lists the assembly as a tree, so you can hide parts to see inside or isolate one part. You can then save what is shown as STL for a 3D printer, OBJ, or GLB for Blender and web viewers. The file is read on your computer and never uploaded. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline. For STL, OBJ, PLY or GLTF meshes, use the 3D Model Viewer.
- How do I convert a STEP file to STL for 3D printing?
- Open it here and choose Save STL. The STL is binary and in millimetres, which Cura, PrusaSlicer, Bambu Studio and other slicers assume. To print one part of an assembly, click "only" beside it in the tree first. Curves become small flat triangles in an STL; this page uses a fine setting, so round holes and fillets stay smooth for printing.
- What is the difference between STEP and STL?
- STEP stores exact geometry: a hole is a true cylinder, with the part names and assembly structure kept. STL is only a mesh of triangles with no units, names or colours, which is what slicers and most 3D tools want. You can turn STEP into STL here, but not back again: an STL has lost the exact surfaces.
- Why is my model lying on its side?
- CAD programs disagree about which way is up. SolidWorks and Fusion 360 usually use Y as up, while CATIA, NX, Creo and FreeCAD use Z. Switch Up between Z and Y under the model. A GLB you save follows the choice, so it stands up the same way in Blender.
- Can I open SolidWorks, Inventor or Fusion files here?
- Not directly: .sldprt, .ipt, .f3d and other native CAD files are closed formats. Export the model as STEP from the program that made it (File, Save As or Export, then STEP AP214 or AP242) and open that here. Anyone you're sharing with can then open it too.
- Is my design uploaded anywhere?
- No. The CAD engine is downloaded to your browser and the model is read and converted there, so a part under NDA or an unreleased product never leaves your computer.