Convert STL to SKP
SketchUp imports STL through File, Import, and saving afterwards gives you the .skp. The import itself is quick. The work is in the two things that go wrong: the model arrives covered in triangle edges, and it arrives at whatever size SketchUp guessed.
We cannot write .skp files. The format is Trimble’s and needs their own SDK, which has no browser build, so only SketchUp saves one. What we can do is prepare the STL so the import goes well: thin it, mend it, and check its real size.
Importing an STL into SketchUp
Written for the current desktop version of SketchUp, where STL import is built in. SketchUp Make 2017 and earlier need the free SketchUp STL extension from the Extension Warehouse, which adds the same menu entry.
Start the import
File → Import…
A file browser opens. Nothing with an .stl extension will be listed until you change the file type, which is the next step.
Choose the STL file type
File type: STereolithography Files (*.stl)
With the type set, select your file but do not press Import yet. The Options button beside the type list holds the two settings that decide how usable the result is.
Set the options
Options… → Merge coplanar faces (tick) · Units: Millimeters
Merge coplanar faces removes the diagonal edges across flat surfaces, so the side of a box arrives as one face instead of two triangles. Units tells SketchUp what the numbers in the file mean.
The unit is the one people get wrong. An STL records no unit, printing files are almost always millimetres, and SketchUp’s templates are often in inches. Left on the wrong setting, a 50 mm part arrives 50 inches wide.
Import, and check the size
Import → then Tape Measure tool (T) across a known dimension
The model arrives as a single group. Measure something you know the size of. If it is wrong by a factor of 25.4, undo and import again with the other unit rather than scaling by eye.
Soften the remaining edges
Open the group → Select All → right-click → Soften/Smooth Edges
Curved surfaces still show every triangle edge. Soften Edges hides them and shades across them, with a slider for the angle below which an edge is hidden. Around 20 degrees smooths curves while keeping real corners sharp.
Save the model
File → Save As…
That is the .skp. Check Entity Info for the group first: if it says Solid Group, the mesh is closed and SketchUp’s solid tools will work on it.
Why an imported STL looks like a wireframe
SketchUp draws an edge wherever two faces meet. A model built in SketchUp has few faces and few edges, because a wall is one face. An STL is triangles and nothing else, so a single flat wall arrives as two faces at least and a curved surface as hundreds, each one outlined.
Nothing is wrong with the geometry. It is the same shape, drawn by a program that shows you every edge. Two things fix the appearance. Merging coplanar faces removes edges that separate faces lying in the same plane, which cleans up every flat region. Softening hides the edges on curved regions without removing them.
If you imported without the merge option, the free CleanUp³ extension from the Extension Warehouse does the same job afterwards, and removes stray edges and duplicate faces while it is there.
What will not happen is the STL turning back into clean SketchUp geometry you can push-pull. A cylinder is still forty flat strips. Push-pull works on a single flat face, so it works on the merged flat regions and not on anything curved.
Thin a heavy mesh before importing
SketchUp is built for models with thousands of faces, not millions. It keeps every edge and face as a separate entity it can select and snap to, which is what makes it pleasant to draw in and what makes it slow on dense meshes.
A sculpt or a 3D scan with half a million triangles can take many minutes to import, and the result orbits at a frame or two a second. Somewhere around a hundred thousand faces is where most machines begin to struggle.
So reduce the file first. The reduce tool on this site cuts the triangle count in your browser and shows the model before and after, and a mechanical part often loses ninety percent of its triangles with no visible change. Do this before the import; SketchUp has no built-in decimation.
Making the import a solid
If the point of bringing the STL into SketchUp is to modify it and print it again, it has to be a solid in SketchUp’s sense: a group whose faces enclose a volume with no holes, no stray edges and no faces inside. Entity Info says Solid Group when that is true.
An STL that was printable going in is usually solid coming out. When it is not, the cause is nearly always in the file — a small hole, or surfaces that pass through each other — and it is easier to find and mend before importing than after. Check the file here for open edges, repair it if it has any, and import the repaired copy.
Inside SketchUp, the free Solid Inspector² extension highlights whatever is stopping a group being solid. The web version of SketchUp cannot install extensions, so for anything beyond a clean, light STL the desktop version is the one to use.
Where we can actually help
The preparation runs here in your browser. Thin the mesh so SketchUp can handle it, mend it so it arrives as a solid, and if the model is not an STL yet, make it one.
- 3MF to STL.3mf → .stl
- OBJ to STL.obj → .stl
- GLB to STL.glb → .stl
- STEP to STL.step → .stl
- Reduce the size of an STL fileFewer triangles, the same shape, a much smaller file
- Repair an STL that will not sliceClose the holes and separate the bad edges so a slicer accepts it
- Check whether an STL is ready to printFind out what is wrong with a model before you print it
Questions
- Can SketchUp open STL files?
- Yes. File, Import, then set the file type to STereolithography Files (*.stl). Open Options before importing to merge coplanar faces and set the unit.
- Is there an online STL to SKP converter?
- Not one that runs in your browser. Only SketchUp writes .skp files. Importing the STL into SketchUp and saving is the conversion, and it takes about a minute.
- My imported STL is far too big or too small.
- The import unit did not match the file. STL files for printing are almost always in millimetres. Undo, import again, and set Units to Millimeters under Options.
- How do I get rid of all the triangle lines?
- Tick Merge coplanar faces in the import options to clear flat areas, then select everything inside the group, right-click, and use Soften/Smooth Edges for the curved areas.
- SketchUp freezes when I import the STL.
- The mesh has too many triangles. Reduce it to well under a hundred thousand first, then import the smaller file.
Where to go next
Related guides
Tools that do part of this here
About these formats
Checked against current software versions on 2026-10-09