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OBJ to STEP Converter

Turn an OBJ mesh into a STEP (.stp) solid that keeps named bodies and material colors. Repairs gaps and rebuilds holes as true cylinders. Free, private, runs in your browser.

Convert an OBJ file

OBJ mesh file

Upload model

Optional: to export material colors

No file at hand?

Units used in the OBJ file

Face handling

Merge coplanar triangles into planar faces Recommended. Smaller file and cleaner CAD faces.

Curved surfaces

Recognize cylinders (holes, slots, fillets) Recommended. Fewer faces and recognizable holes.

Output file name

Conversion runs locally in this browser tab. Your file is never uploaded.

STEP output

Load an OBJ file to start

Watertight meshes export as solid bodies. Meshes with gaps export as surface models, and the mesh check explains what to fix.

Drop an OBJ file or click to browse .obj · up to 100 MB · up to 1,200,000 triangles

No file at hand?

Optional: to export material colors

Conversion runs locally in this browser tab. Your file is never uploaded.

Converted geometry is for reference only. It is built from an OBJ mesh and can differ slightly from the original design, so we do not recommend it for for CNC machining, sheet metal, CAM, or tooled production; use a natively designed STEP file for those. Xometry assumes no liability for results from using converted files in production.

How does OBJ to STEP conversion work?

Clean and repair the mesh

The converter triangulates quads and polygons, welds duplicate vertices per body, removes zero-area triangles, aligns triangle winding, splits non-manifold pinch vertices, and caps small flat gaps automatically.

Simplify if needed

Meshes above 300,000 triangles are simplified to that size (up to 1,200,000 are accepted). Open boundaries, body borders, and color borders are kept.

Build faces, cylinders, and bodies

Coplanar, same-colored triangles merge into one planar face. Strips that lie exactly on a cylinder, or on a cone around the main axis, become one true curved face with circular edges. Everything else stays flat. Each named OBJ object (or group) becomes its own solid.

Write STEP AP214

Closed shells are written as solid bodies (MANIFOLD_SOLID_BREP) with colors from OBJ vertex colors or the attached MTL file. Open meshes are written as surface models, which quoting systems usually reject.

FAQ

How do I convert an OBJ file to STEP online for free?

Drop your .obj file on the converter, attach the .mtl file if you want material colors, select the unit the model was made in, and press Convert to STEP. You get a solid STEP file (AP214) for CAD, re-modeling, and CNC machining quotes. This mesh to STEP conversion needs no account.

Is the STEP file a real solid I can machine?

CAD software can measure and section it, and quoting systems can read it. Holes, slots, and fillets that match a cylinder exactly are true cylindrical faces. Other curved areas stay as flat facets. Treat the file as a reference model and check dimensions in CAD before any production use.

Why is my result a surface model, or why did my STEP file fail to upload?

A solid needs a closed mesh where every edge is shared by exactly two triangles. If the mesh check still shows open edges, close the gap in a mesh tool such as Blender or Meshmixer and convert again. A surface model will not upload to the Xometry Instant Quoting Engine®, which needs a solid. Files with over 12,000 faces or 15 MB can also be rejected. In that case, ask for the native CAD file.

Why are some holes and fillets cylinders and others flat facets?

The converter rebuilds a cylinder or cone only when the triangles lie on it exactly and every edge can be written as an exact circle or line. Spheres, tori, freeform blends, chamfered holes away from the main axis, and holes that meet a fillet stay flat, because a partial curve would stop CAD from building a solid. Turn off Recognize cylinders to keep flat facets everywhere.

What mesh repair happens automatically, and what does not?

Automatic: welding duplicate vertices per body, removing degenerate triangles, splitting non-manifold vertices, and capping small flat gaps. Not automatic: filling large or curved holes or fixing self-intersections, which would mean inventing geometry. The mesh check lists what was repaired and what remains.

Does the converter export multiple bodies?

Yes. Each named OBJ object (o) becomes its own named solid. Without o lines, groups (g) are used instead. Bodies never share a vertex or edge, even if they touch, and disconnected shells inside one group get unique names.

Are colors, textures, and materials kept?

Vertex colors (v x y z r g b) and MTL material colors (Kd) are written as STEP face colors. Attach the .mtl file next to the .obj, because the browser cannot read it on its own. Textures and UV coordinates are not transferred, since a machining STEP file has no use for them.

What happens to very large OBJ meshes?

Up to 300,000 triangles convert directly. Up to 1,200,000 triangles are simplified to 300,000 first, which can reduce the number of recognized cylinders, and a notice appears. Above 1,200,000, decimate the mesh in your modeling tool first.

What units does the STEP file use?

The STEP file is always in millimeters, so SolidWorks, Fusion 360, Creo, NX, and other CAD systems open it at the correct size. OBJ files have no units, so you select what the numbers in your file mean. Example: 88 with cm selected becomes 880 mm. If the bounding box looks 10 or 1000 times off, change the unit.

Why is the STEP file larger than my source mesh?

STEP stores every face, edge, and vertex as a separate text record, so a triangulated STEP file is typically 5 to 15 times larger than the OBJ. Merging flat triangles and rebuilding cylinders reduces this.

Is the OBJ to STEP converter free, and is my file uploaded anywhere?

It is free, and your file is never uploaded. Everything runs in a background thread in your browser tab, so confidential designs stay on your computer.