Free online STL to IGES converter

Older CAD, inspection, and manufacturing systems may require IGES when the available model is an STL from a scanner, slicer, or 3D-printing workflow. Converting it can satisfy an import requirement, but it cannot restore the original parametric CAD model or design history.

What the STL format is

STL stores a surface as triangular facets defined by vertex coordinates and an intended normal direction. It does not contain native units, feature history, sketches, constraints, tolerances, colors, materials, or analytic definitions for planes, cylinders, and spheres.

CAD programs, 3D scanners, slicers, reverse-engineering systems, simulation tools, and mesh applications commonly create or use STL files. Binary STL is the usual compact form; ASCII STL is human-readable but substantially larger. STL normals can be missing or incorrect in practice, so converters often recalculate or repair them.

What the IGES format is

IGES, normally saved with an .igs or .iges extension, is a neutral CAD exchange format for entities such as points, curves, wireframes, trimmed surfaces, and, in some implementations, solid boundary representations. It is still used by suppliers, CNC, inspection, and legacy CAD systems that do not accept newer formats.

IGES can describe mathematical curves and surfaces instead of only triangles, but it does not preserve a model's feature tree or parametric constraints. STEP is generally the better choice for modern solid-model exchange when the receiving system supports it.

How to convert an STL file to IGES

Using CAD Exchanger

CAD Exchanger is a commercial desktop option that imports STL and exports IGES without requiring the original CAD application.

1. Open the STL and check its orientation, bounding-box dimensions, and apparent scale.
2. Repair open boundaries, non-manifold edges, self-intersections, duplicate triangles, and inconsistent normals. Use the application's repair tools or a mesh utility such as MeshLab or Microsoft 3D Builder before conversion.
3. Choose File → Export, select IGES (*.igs, *.iges), and choose the available surface or faceted-geometry settings.
4. Open the exported file in the destination CAD system. Check dimensions, missing faces, gaps, normals, and face count rather than assuming that a successful export is geometrically valid.

Using FreeCAD

1. Open FreeCAD and switch to the Part workbench.
2. Choose File → Import and load the STL.
3. Select the mesh and use Part → Create shape from mesh. Set a tolerance appropriate to the model: a value that is too small can leave gaps, while a large value can change the geometry.
4. If the resulting shell is closed and watertight, select it and use Part → Convert to solid. This step is optional and will fail or produce an unusable result for an open or defective mesh.
5. Select the resulting shape and choose File → Export, then select IGES (*.igs, *.iges).

FreeCAD is practical for clean, modest-sized meshes. Dense scans can become thousands or millions of triangular IGES faces, making the file slow to open or unusable in the receiving system.

Using online conversion

CAD Exchanger Cloud provides an online option for non-confidential files: upload the STL, select IGES, download the result, and validate it in the target application. Online services may impose file-size, face-count, or account limits, and their conversion settings can be less controllable than desktop software. Do not upload proprietary parts, customer data, tooling, or personal scans unless the service's storage, retention, and security terms are acceptable.

Quality and compatibility limitations

The conversion cannot recover design intent. It can only reinterpret the triangles present in the STL. A flat region may become many triangular planar faces, and a curved surface retains the STL's tessellation error rather than becoming the exact original cylinder, cone, or NURBS surface.

STL does not store units. Compare the imported bounding-box dimensions with the intended dimensions before export; a part intended to be 25.4 mm can be interpreted as 25.4 inches by software using a different unit assumption. Apply the correct scale before creating the IGES file.

A watertight, consistently oriented mesh is needed for reliable solid creation. Holes, flipped normals, intersecting triangles, degenerate facets, and non-manifold edges can produce missing IGES faces, gaps, or a surface-only result. Some IGES readers also handle trimmed surfaces and solid entities differently, so test the file in the exact downstream system.

For machining, redesign, or feature editing, use reverse-engineering software such as Geomagic Design X, Mesh2Surface for Rhino, or equivalent tools to fit planes, cylinders, and NURBS surfaces to the mesh. If the source CAD model exists, export that model directly to IGES or STEP instead of converting its STL derivative.