SKP File Documentation

Summary

An SKP file is the native document of SketchUp, the 3D modelling program now owned by Trimble. It stores a full model: edges and faces, grouped components, materials, tags and saved scenes. Its MIME type is application/vnd.sketchup.skp. The format is version-specific, so a file saved in a newer SketchUp will not open in an older one, which is the most common reason a .skp “won’t open”. For 3D printing, export the model to STL or OBJ.

Technical details

Feature	Value
Full name	SketchUp Document
File extension	`.skp`
MIME type	`application/vnd.sketchup.skp`
Format type	Proprietary binary 3D model, version-specific
Developer	Trimble Inc. (originally @Last Software, then Google)
Introduced	2000 (SketchUp 1.0, @Last Software)
Current owner	Trimble (since 2012; Google 2006–2012)
Open standard	No — proprietary; read/write via the SketchUp SDK
Byte order	Little-endian
Version header	UTF-16LE version string near the start (e.g. “SketchUp Model”)
Magic (recent files)	`FF FE FF 0E` then UTF-16LE version string (version-dependent)
Stores	Geometry, components, materials, textures, tags, scenes, camera
Companion format	`.skb` (automatic backup), `.layout` (LayOut document)
Backward compatibility	Newer SketchUp opens older files; older cannot open newer
Save-down	File › Save As lets you write an older SketchUp version
3D-print export	`.stl` (built in, also in SketchUp Free)
Interchange export	`.obj`, `.dae`, `.fbx`, `.dwg`, `.dxf` (SketchUp Pro)
Related extensions	`.skb`, `.layout`, `.stl`, `.obj`, `.dae`, `.dwg`
SDK / spec	`developer.sketchup.com`

Structure at a glance

SKP is a proprietary little-endian binary format with no single fixed magic number: the header layout changes between file versions. What is stable is a UTF-16LE version string near the start of the file (for example “SketchUp Model”), which identifiers use to recognise the file and its version. Recent files commonly begin FF FE FF 0E followed by that string. Because the on-disk layout is versioned and undocumented, tools read and write SKP through Trimble’s official SketchUp SDK rather than by parsing bytes directly.

What is an SKP file?

An SKP file is the native document format of SketchUp, a 3D modelling program first released in 2000 by @Last Software. Google bought SketchUp in 2006 and ran the free “Google SketchUp” era, then sold it to Trimble in 2012, the current owner. A single .skp holds one complete model: the edges and faces that form the geometry, reusable component definitions, groups, materials and image textures, layers (called tags), and saved scenes with their camera positions and styles. SketchUp is used across architecture, interior and landscape design, woodworking, set design and, increasingly, 3D printing, largely because its push/pull modelling is quick to learn.

SKP is proprietary and binary. Trimble does not publish the on-disk byte layout; instead it ships the SketchUp SDK, a C API that reads and writes the format, so third-party applications integrate against the SDK rather than parsing the file directly. The single most important practical fact about the format is that it is version-specific, and that shapes almost everything about how the files behave in the wild.

The version header and why old SketchUp rejects new files

Every .skp is tagged with the SketchUp version that wrote it. Near the start of the file is a UTF-16LE version string (for example “SketchUp Model”), which is how tools identify both that the file is an SKP and which release produced it. The compatibility rule is one-directional: a newer SketchUp opens files from older releases, but an older SketchUp cannot open a file saved by a newer one. When that happens the program reports an “unsupported version” error.

This versioning, not corruption, is the usual cause of a .skp that “won’t open”. The fix is to have the file re-saved from a compatible release: SketchUp’s File › Save As lets the author pick an older SketchUp version to write, producing a file the older installation can read. The browser-based SketchUp Free always tracks the current release, so it can open recent files that a years-old desktop install rejects.

Inside the model: geometry, components, materials and scenes

The model data inside an .skp is organised into several kinds of content, and understanding them explains what survives an export and what does not.

Element	What it holds
Geometry	Edges and the faces bounded by them; SketchUp’s surfaces are flat polygons
Components & groups	Named, reusable component definitions and grouped geometry; instances reference one definition
Materials & textures	Face colours and embedded image textures with their UV placement
Tags (layers)	Visibility and organisation of geometry; geometry still lives in the model, tags control display
Scenes	Saved camera views, styles, shadow settings and animation transitions
Version header	The SketchUp release that wrote the file, which gates compatibility

Two properties of SketchUp geometry matter when the model leaves the format. First, SketchUp models with edges and faces, not solids by default: a shape is “solid” only when its faces fully enclose a watertight volume with no stray edges or holes. Second, components are stored once and instanced many times, which keeps files small but means an export that flattens instances can multiply the polygon count. Both facts drive the behaviour of exports for 3D printing and for other 3D software.

Component definitions and instances

Components are the core of how SketchUp keeps large models manageable. A component definition stores the geometry once; each place the component appears in the model is an instance that references that definition plus a transform (position, rotation, scale). Editing the definition updates every instance at once. Groups are a lightweight version of the same idea for geometry you do not intend to reuse. When you export to a mesh format, the exporter walks these instances and bakes each one into concrete triangles, which is why a model that was compact on disk can produce a much larger OBJ or STL.

Exporting to STL, and what “solid” means to a slicer

SKP is a working format, not a delivery format, so using a model elsewhere means exporting to a neutral format. For 3D printing the target is STL, and SketchUp can write it directly through File › Export (STL export is available even in the free web tier). A slicer needs a manifold mesh: every edge shared by exactly two faces, no holes, no internal faces. In SketchUp terms the exported geometry must be a solid group or component, which SketchUp reports in the Entity Info panel. If it is not solid, the slicer will reject the STL or produce a bad print, so the standard workflow is to make the model a solid before exporting.

STL carries only triangles: no colour, no materials, no units beyond the raw coordinates. That is fine for a single-material print but loses the model’s appearance, which is where the other export formats come in.

OBJ, DAE, FBX and DWG: taking the model to other software

To move a model into Blender, a game engine or another CAD package, SketchUp Pro exports several interchange formats, each preserving different data. OBJ carries geometry plus materials and UV texture coordinates, which makes it the common choice for rendering and for Blender. DAE (COLLADA) and FBX add scene structure and are aimed at game engines such as Unity and Unreal and at the 3ds Max/Maya pipeline. DWG and DXF export to AutoCAD for 2D plans or 3D CAD work. A limitation to know: SketchUp Free (web) exports only STL and image formats; OBJ, FBX, DAE and DWG require a paid SketchUp Pro tier. If you only have the free web app, the practical route is to export STL and convert, or use a dedicated converter.

.skb backups and file recovery

Alongside a saved .skp, SketchUp keeps an automatic backup with the extension .skb. It is the previous saved state of the model, written each time you save so that a corrupted or lost .skp can be recovered. If a model fails to open, renaming the matching .skb to .skp often restores the last good version. SketchUp also autosaves at an interval you set, which protects against crashes between manual saves.

Frequently asked questions

Why won’t my SKP file open?

Almost always a version mismatch: the file was saved in a newer SketchUp than the one you have, and older releases cannot read newer files. Ask the sender to use File › Save As and choose an older SketchUp version, or open the file in SketchUp Free, which always tracks the current release.

How do I convert an SKP to STL for 3D printing?

Use File › Export › STL, which is available in both SketchUp Free and Pro. Make the model a solid group or component first, checked in Entity Info, so your slicer accepts the mesh. STL keeps only the triangles, no colour or materials.

How do I get an SKP into Blender?

Export from SketchUp Pro to OBJ, DAE or FBX and import that into Blender. SketchUp Free can only export STL of those options, so from the free tier you export STL, or use a converter, and lose the materials.

What is the .skb file next to my model?

It is SketchUp’s automatic backup, the previous saved state of the model. If your .skp is damaged, rename the matching .skb to .skp to recover the last good version.

References

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