How to Smooth Edges in SketchUp: Soft, Smooth & Hidden

• Right click – softened and smoothed edges – check box smooth normal
• At zero of smooth value, all planes is rough
• When value of smooth is increased , all planes have been smoothed

  

The slider you are dragging is labelled Angle between normals: it does not smooth everything blindly, it only affects edges where the angle between the two adjacent faces is smaller than the value you set. That is why a low setting leaves sharp corners alone while a high setting “rounds” the whole shape — SketchUp is hiding edges below the angle threshold, not changing the geometry. The mesh underneath is exactly the same; only the shading changes.

Soft vs Smooth vs Hidden in SketchUp — they are not the same thing

This trips up most beginners. Softening an edge hides it AND fuses the two faces into a single “surface” entity, so a click selects the whole curved area at once; smoothing only adds the shading that blends the two faces visually. Hiding (Shift while erasing) makes the edge invisible too, but it does not merge the faces into a surface. In the Soften/Smooth panel the “Smooth normals” box is what controls that blended shading — clear it and edges are still softened (hidden), but each facet keeps its own flat shading.

The fast way to smooth edges in SketchUp: the Eraser tool, not the dialog

For a few edges you do not need to open the window at all. Pick the Eraser (press E) and hold Ctrl (Option on macOS) while dragging over the edges to soften/smooth them; hold Shift to hide instead; and Ctrl+Shift while erasing un-softens edges you already smoothed. To get hidden/softened edges back for editing, turn on View > Hidden Geometry so they reappear as dashed lines you can select.

Gotchas worth knowing

“Soften coplanar” deletes the edges between flat faces entirely — useful for cleaning up tessellated imports, but it permanently merges faces that were split, so only tick it when you actually want those dividing lines gone. Also note that softened edges no longer cast their own shadow lines and are skipped by most line-style exports, which is exactly why smoothing a curved surface looks clean in renders. If softening seems to do nothing, the edges are almost always sitting inside a group or component — you must double-click in to edit that context first, because the operation only applies to edges in the currently open context.