Free online STEP (.step/.stp) converter. Convert STEP CAD files to STL, GLB, glTF, OBJ, PLY in your browser — no upload, no watermark.
.step or .stp model, or click "Choose 3D file". The first time you open the converter it loads an OpenCASCADE CAD engine (occt-import-js) into the page, a one-time download of roughly 7-8 MB; after that, conversions run instantly on your own device.<model-viewer> embedsSTEP stands for STandard for the Exchange of Product model data, the international CAD interchange format defined by ISO 10303. The .step and .stp files most people have are the clear-text encoding from Part 21 of that standard (ISO 10303-21), first published in 1994. STEP is the neutral format that SolidWorks, Autodesk Fusion 360, CATIA, Onshape, FreeCAD, and most other CAD systems use to hand a design to one another without locking it to one vendor.
The reason STEP is so precise is also the reason you often have to convert it. A STEP file is a boundary-representation (B-rep) model: it stores geometry as exact mathematical surfaces and solids — NURBS curves, trimmed faces, and watertight solid bodies — rather than as triangles. That exactness is perfect for engineering and CAM, but most downstream tools cannot read it:
.glb loads cleanly in <model-viewer>, WebXR, Unity, Unreal, and Three.js, where a raw STEP file simply will not open.Note this converter is one-way: it reads STEP and writes mesh formats. There is no mesh-to-STEP export here, because rebuilding exact parametric B-rep solids from a triangle mesh is a separate reverse-engineering problem, not a file conversion.
| Format | Representation | Editable parametric CAD | Stores color | Best for |
|---|---|---|---|---|
| STEP (.step / .stp) | Exact B-rep solids & NURBS surfaces | Yes (in CAD apps) | Limited (AP242) | CAD interchange, engineering, CAM |
| STL (.stl) | Triangle mesh (tessellated) | No | No | Universal 3D printing / slicers |
| 3MF (.3mf) | Triangle mesh + print metadata | No | Yes (multi-material) | Modern color 3D printing |
| GLB / glTF | Triangle mesh + PBR materials | No | Yes | Web, AR, real-time engines |
| OBJ (.obj) | Triangle/quad mesh (+ .mtl) |
No | Via .mtl |
Blender, Maya, broad mesh interchange |
| PLY (.ply) | Triangle mesh + per-vertex data | No | Per-vertex | 3D scans, point clouds, research |
| STEP data | Carries into the mesh? | What actually happens |
|---|---|---|
| Solid and surface shape | Yes, approximated | The B-rep is tessellated into triangles; the silhouette matches, curves become facets |
| Exact NURBS surfaces and curves | No | Flat triangles replace the surface equations, so nothing downstream can re-derive the true curve |
| Watertight solids | Usually | A closed STEP solid exports as a closed mesh; loose or trimmed surfaces can produce open shells |
| Assembly structure (separate parts) | Depends on the target | glTF/GLB carry a scene graph and OBJ has named objects and groups; STL flattens everything into one triangle soup |
| Colors (AP242 presentation data) | Depends on the target | GLB, glTF, and 3MF can store color; STL cannot, and OBJ needs a companion .mtl |
| Units | Depends on the target | 3MF records units explicitly; STL is unitless and slicers assume millimeters |
| PMI, GD&T, and annotations | No | Tolerances and dimension callouts have no triangle equivalent and are dropped |
| CAD feature tree / parametric history | No | A STEP export already contains the finished solid rather than the modeling history that produced it |
A STEP file stores exact CAD geometry — mathematically precise surfaces and watertight solids (boundary representation, or B-rep). An STL file stores only a triangle mesh that approximates those surfaces. Converting STEP to STL is called tessellation: the smooth NURBS faces are sampled into flat triangles, so an STL is an approximation of the original CAD model, while STEP is the exact model. STEP is what you keep for editing and engineering; STL (or 3MF) is what a 3D printer's slicer actually needs.
Not with this tool, and generally not with any simple converter. STEP describes exact parametric surfaces and solids, while STL, OBJ, GLB, and PLY are triangle meshes with no surface equations. Going from a mesh back to a true B-rep STEP solid means reconstructing those surfaces — a reverse-engineering task that CAD packages like Fusion 360, SolidWorks, or specialized tools handle with manual or auto-surfacing, not a one-click conversion. This converter is import-only: STEP in, mesh out.
It will be a faithful approximation, not a mathematically exact copy. Because STEP stores curved surfaces as equations and meshes store flat triangles, every STEP-to-mesh conversion introduces some tessellation. Flat-faced parts convert essentially perfectly; highly curved or organic shapes show their accuracy in how finely the surfaces are triangulated. For most 3D printing this is invisible at typical layer heights, but for tight engineering tolerances you should verify the mesh against your nominal CAD geometry.
STL for the widest compatibility — virtually every slicer reads it, and it is the safe default for a single-material print. Choose 3MF when you want color, multiple materials, or real-world units to stay with the model; 3MF, published by the 3MF Consortium since 2015, is an XML-and-ZIP package that carries print metadata STL cannot. Both formats discard STEP's parametric editability and keep only the printable mesh.
No. This converter parses and tessellates your STEP file entirely in your browser using the occt-import-js WebAssembly build of the OpenCASCADE CAD kernel — the file is read, converted, and downloaded on your own device, so it never leaves your computer. That means no upload wait, no account, and no watermark. The only network cost is the one-time download of the CAD engine the first time you use the tool.
Most CAD systems read STEP natively, including SolidWorks, Autodesk Fusion 360, AutoCAD, CATIA, Siemens NX, Onshape, and the free FreeCAD. General 3D apps like Blender, however, need an add-on to import STEP, and slicers and web viewers do not read it at all — which is why converting STEP to a mesh format is so common when the destination is a 3D printer, a game engine, or a web page.
For visual fidelity on the web or in a viewer, GLB or glTF preserve the most, since they carry the mesh plus materials in a single modern container. For 3D printing, STL and 3MF carry pure geometry, which is all a slicer needs. In our testing, a mechanical bracket exported to GLB at the default tessellation rendered with smooth-looking filleted edges, while the same part exported to STL produced an equivalent watertight mesh ready to load straight into a slicer. No mesh format, though, preserves STEP's editable parametric solids — for that you must keep the original .step file.
Nothing — they are the same format under two spellings of the same extension, and both normally hold the clear-text (Part 21) encoding defined by ISO 10303-21. The three-letter .stp form exists because older DOS-era filesystems allowed only three characters after the dot, and plenty of CAD systems kept writing it out of habit. You can rename one to the other and any CAD package or converter will read it identically. If a tool accepts one and rejects the other, it is enforcing an extension whitelist rather than detecting a different format, so renaming the file usually gets it loaded.