# CAD Tessellation: When a Solid Becomes a Triangle Mesh

Tessellation approximates CAD faces with triangles for display, STL or glTF. Finer meshes stay approximate and do not restore B-Rep volume.

This guide covers general CAD workflows. CADProps supports STEP, IGES, SolidWorks parts and ZIP assemblies, STL, OBJ, 3MF and static GLB/GLTF. Validated conversions are downloadable. Partial assemblies carry warnings; properties cover loaded geometry only.

Tessellation replaces curved CAD faces with triangles. Viewers do it to draw a model. STL, OBJ and glTF exports do it because those formats store a mesh. The triangles are an approximation. They are not a more precise form of the solid, and they are not a record of the original faces.

A coarse mesh makes a round hole look polygonal. A fine mesh can look smooth and still be a mesh. Increasing the number of triangles does not recover the analytic cylinder, the feature tree or a unit declaration the mesh format never had.

## Where you meet tessellation on this site

The shaded view of a STEP or IGES model is a display mesh. Properties for those formats are calculated from B-Rep when that geometry is available, not from how finely the picture was triangulated. [What B-Rep means](https://www.cadprops.com/guides/what-is-brep/index.md) separates the two.

A [STEP to STL](https://www.cadprops.com/tools/step-to-stl/index.md) file is a tessellated delivery. STL and OBJ coordinates are assumed to be millimetres because those formats do not reliably declare a unit. 3MF can carry a declared unit that is converted to millimetres. glTF is in metres and is normalized to millimetres for measurement. In every mesh case, dimensions and area are approximate, and volume exists only for a closed, consistent mesh.

## What changes when the mesh gets finer

Chord height, angle and other export tolerances decide how far the triangles may stray from the source face. Those settings are the control. Adding decimal places to the filename is not.

Finer tessellation usually means:

- a closer visual match on curves;
- a larger file;
- a mesh measurement that can change slightly, because the approximation changed.

It does not mean the mesh volume has become the B-Rep volume. For the published synthetic block, the STEP solid is 40 × 30 × 20 mm, with volume 24,000 mm³ and area 5,200 mm². Those figures are the analytic solid in the [sample library](https://www.cadprops.com/examples/index.md). They are not a measured error table for customer uploads, and they are not a promise that an STL of a different part will match its source to a stated percentage. This site does not publish aggregate statistics from real customer files.

If you need the solid's volume, measure the STEP or other B-Rep. If you need a print mesh, export STL at a tolerance the process accepts and check one known dimension after import. [STL export settings](https://www.cadprops.com/guides/stl-export-settings/index.md) covers resolution separately from units.

## Checks after tessellation

1. Record the source revision and the export tolerance if you know it.
2. Open the mesh in the [STL viewer](https://www.cadprops.com/tools/stl-viewer/index.md) or the matching mesh tool.
3. Compare one known length with the CAD model. A 25.4 factor is an inch/millimetre problem, not a triangle-count problem.
4. Confirm the mesh is closed before using volume. [Watertight meshes](https://www.cadprops.com/guides/watertight-cad-mesh/index.md) explains why a visible part can still have no volume.
5. Keep the original STEP or native file. A later request for precise geometry cannot be answered from the triangles alone.

Mass from a mesh is the approximate volume times a density you choose. Both inputs have to be stated, or the mass is not interpretable.

## Related reading

- [3MF vs STL: Units, Multiple Parts and Mesh Handoff](https://www.cadprops.com/guides/3mf-vs-stl/index.md)
- [STEP vs STL: CAD Measurement, Geometry and Accuracy](https://www.cadprops.com/guides/step-vs-stl/index.md)
- [STEP vs STP Files: Extensions and CAD Compatibility](https://www.cadprops.com/guides/step-vs-stp-file-extension/index.md)
- [STL Export Settings: Mesh Resolution, Units and Scale](https://www.cadprops.com/guides/stl-export-settings/index.md)
- [Watertight Mesh: When an STL Can Have a Volume](https://www.cadprops.com/guides/watertight-cad-mesh/index.md)
- [What B-Rep Means in a STEP or IGES File](https://www.cadprops.com/guides/what-is-brep/index.md)
- [STL Volume Zero or Missing? Check the Mesh Is Closed](https://www.cadprops.com/guides/why-stl-volume-is-zero/index.md)

Original article: https://www.cadprops.com/guides/cad-tessellation/

HTML page: https://www.cadprops.com/guides/cad-tessellation/