What is a .skp file?

What is inside a SketchUp file

SketchUp does not model solids the way a mechanical CAD package does. A model is a collection of edges and the flat faces they bound. A curved surface is many narrow flat faces with their shared edges hidden or smoothed, and a "solid" in SketchUp is a group whose faces happen to close a volume. The file stores exactly that: edges, faces, and the grouping that turns them into components.

That is why an SKP behaves like a mesh format when it leaves SketchUp. Export it to COLLADA, OBJ or STL and you get polygons, because polygons are all there ever were. There is no NURBS surface underneath waiting to be recovered.

What the format carries beyond geometry is generous. Materials with textures, per-face front and back. Layers, called tags since SketchUp 2020. Components with their definitions stored once and placed many times, which keeps a file with a thousand identical chairs small. Scenes, section planes, dimensions and text. Geolocation and the shadow settings that depend on it. And a unit, set in Model Info, that every importer reads back.

Versions

Until 2020, each yearly SketchUp release wrote its own file version, and an older SketchUp could not open a newer file at all. The workaround was "Save as" with an older version chosen in the dialog.

SketchUp 2021 replaced that with a versionless format that Trimble describes as both forward and backward compatible, so any file saved by 2021 or later opens in 2021 or later. The 2024 release then removed the option to save down to the pre-2021 formats altogether. Someone still running SketchUp 2020 or earlier therefore cannot receive a current file at all, and Trimble's own advice is to open it in SketchUp for Web, which is free.

The binary layout itself is not published. Trimble ships a C SDK that reads and writes it, and that SDK is what Rhino and the other third-party importers link against. There is no independent open-source reader of any completeness.

Where SKP files come from

Architecture and interior design, first. SketchUp is the sketching tool of a large share of the architectural profession, and the 3D Warehouse it ships with holds millions of SKP models of furniture, fixtures and buildings, which is where most SKP files people receive originate. Woodworkers and set designers use it heavily. It is rare in mechanical engineering.

Getting geometry out

SketchUp's own exporters are the reliable route. COLLADA is the default and keeps materials and the component hierarchy. OBJ, FBX and 3DS are available in the Pro licence, and STL export is built in for printing. The free web version exports STL and a handful of image formats.

For 3D printing, check that the model is a closed group before exporting, and check the unit: SketchUp's default template is inches for some regions and millimetres for others, and a model drawn in the wrong template prints at the wrong size after an STL export, since STL cannot say which was meant.

For CAD exchange, the paid plans export DWG and DXF, and what arrives is the polygon faces as flat faces. There is no way to make a curved surface smooth again on the receiving side, because SketchUp never had one. If a CAD user needs a solid, a STEP from a SketchUp-reading CAD package such as Fusion or Rhino is the route, and it will be a faceted one.

How to open a .skp file

SketchUp Free opens a .skp in a browser tab at no cost, and Autodesk Viewer displays one in a browser without any SketchUp account. Trimble Connect's free viewer opens files saved by SketchUp 2021 or earlier. This site cannot read SKP.

Rhino, Archicad and Revit import SKP directly, and Fusion opens it under its free personal-use licence. Blender does not read it; the route there is a COLLADA or OBJ export from SketchUp, which needs a paid plan, or an STL from the free web version.

Since SketchUp 2021 the file format has been versionless, so a 2026 file opens in 2021. SketchUp 2020 and earlier each had their own format and refuse a newer file, and since the 2024 release SketchUp can no longer save down to those versions. If you are stuck on an old copy, SketchUp Free in the browser opens the file.