Free online STL to IGS converter

A supplier, older CAD system, or surface-modeling application may require an .igs or .iges file instead of an STL. Conversion makes the mesh transferable, but it does not restore the precise surfaces, dimensions, or parametric history that the STL does not contain.

What the STL format is

STL represents a 3D object as triangular facets. It stores triangle vertices and may store facet normals, but normally contains no true curves or surfaces, design history, materials, assembly structure, or dependable unit definition.

STL is common in 3D printing, rapid prototyping, 3D scanning, reverse engineering, and mesh inspection. Slicers such as UltiMaker Cura and PrusaSlicer use it, while applications including Blender, FreeCAD, Fusion, SolidWorks, and MeshLab can import or export it.

Binary STL is usually smaller than ASCII STL, but both describe the same faceted geometry. A visually smooth model can still consist of thousands of planar triangles.

What the IGS format is

IGS, also written as IGES and commonly saved with the .igs or .iges extension, is based on the Initial Graphics Exchange Specification. It can contain points, curves, wireframes, trimmed surfaces, and other CAD entities exchanged between different engineering systems.

IGES remains useful with older or mixed CAD systems, surface-modeling software, tooling workflows, and suppliers that specify it as their exchange format. It can represent CAD faces more appropriately than an STL mesh, but it is an older standard; STEP is often preferable when both systems support it.

STL-to-IGES conversion normally creates one planar IGES face from each mesh triangle. The result is therefore a faceted surface or faceted solid, not a native model containing editable cylinders, fillets, sketches, dimensions, and feature history.

How to convert STL to IGS

FreeCAD desktop method

FreeCAD is a practical free option for converting a mesh into an IGES-compatible Part shape.

1. Keep an untouched copy of the STL, then open it in FreeCAD with File → Open or File → Import.
2. Switch to the Part workbench and select the imported mesh in the model tree.
3. Choose Part → Create shape from mesh. Set a tolerance appropriate to the model; an excessive value can change small features, while an unnecessarily small value can increase processing time.
4. If the mesh is watertight, select the resulting shape and choose Part → Convert to solid. If this fails, export the shape as an open or closed surface instead of forcing a solid.
5. Use Part → Refine shape only when useful. It can remove some redundant edges, but it does not merge STL facets into accurate planes, cylinders, or other analytic surfaces.
6. Select the resulting shape and choose File → Export. Save it as model.igs or model.iges; choose an IGES option if FreeCAD displays a format selector.
7. Reopen the exported file in FreeCAD or the receiving CAD system and check dimensions, units, face gaps, surface orientation, and whether the result is a solid or only a surface.

For a large mesh, repair it and remove unnecessary triangles in MeshLab or Blender before conversion. Decimation reduces processing time and file size but can remove detail.

Commercial and online options

Fusion can import an STL, convert a mesh to a BRep with its mesh-conversion tools, and export the resulting body through File → Export when IGES is offered for the selected object and workspace. High-triangle meshes can make this conversion slow or unusable, so repair or simplify the mesh first.

CAD Exchanger Desktop supports STL and IGES in editions that include those formats and is suitable for repeat or batch conversions. Open the STL, select IGES as the output, configure units or healing options when available, export, and verify the result in the destination CAD application.

CAD Exchanger Cloud is an online option for non-confidential, moderate-size files when its current format list includes both STL input and IGES output. Upload the file, select IGS or IGES, download the result, and validate it before use. Do not upload proprietary, regulated, or customer data unless the service terms and organizational policy allow it.

Quality and compatibility limitations

• Check units before conversion. STL does not reliably identify whether dimensions are millimeters, inches, or another unit. Set the correct scale during import or conversion; an incorrect assumption can produce a model 25.4 times too large or too small.
• Triangle density controls the result. Coarse facets produce visibly angular or dimensionally inaccurate surfaces. Excessive density creates very large IGES files and can overwhelm CAD importers. Conversion cannot recover detail missing from the STL.
• A watertight, consistently oriented mesh is needed for dependable solid creation. Holes, self-intersections, duplicate facets, non-manifold edges, and inverted normals can produce an open IGES surface or cause conversion to fail.
• Many IGES files made from STL contain thousands of separate faces. Some receiving applications import them slowly, display them only as surfaces, or reject them. Test the file in the exact destination software.
• For precise design edits, remodel the part from measured references with sketches, planes, analytic surfaces, and parametric features. Direct conversion is mainly geometry transfer, not reverse engineering.