CAD tip # 8754:

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Thumbnail settings can influence AutoCAD DWG file size.

AutoCAD version 2013 has changed the method of storing raster thumbnail images (previews) inside DWG files. These thumbnails are now internally stored in better quality (PNG format) and they have higher default resolution. Windows Explorer or EDM systems working with document thumbnails can now quickly display better pictures of the contents of your DWG drawings.

Size of the thumbnails saved with a drawing is controlled by the THUMBSIZE variable (stored in Registry, default=3). Higher values than the default "3" are by default applied only on 3D drawings. This can be overridden with enabling the variable THUMBSIZE2D.

How does this setting influence the total size of DWG files?

Especially with simple smaller drawings, the increase of the total file size can be quite substantial - up to 2x of the size without any thumbnail (THUMBSAVE=0). The size is also influenced by other factors, e.g. by image compression or by incremental saving of changes into DWGs. The following sample is not influenced by these factors but still consider it an example only:

THUMBSIZE	Thumb resolution	File size	Size increase
off	N/A	62 276	0%
0	64 x 64	63 555	+2.1%
1	128 x 128	64 579	+3.7%
2	256 x 256	65 603	+5.3%
3	512 x 512	70 723	+13.6%
4	1024 x 1024	83 011	+33.3%
5	1440 x 1440	94 275	+51.4%
6	1600 x 1600	99 395	+59.6%
7	1920 x 1920	108 611	+74.4%
8	2560 x 2560	132 163	+112.2%

In complex DWGs, the total thumbnail (in the largest resolution) can add up to 10MB to the drawing file size.

ACAD2021ACAD2018ACAD2013LT2013DWG

* CAD

9.8.2012 28246×

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applies to: AutoCAD 2021 · AutoCAD 2018 · AutoCAD 2013 · AutoCAD LT 2013 · DWG ·

See also:
Tip 12753:	"Local server is loading" when inserting a block in AutoCAD LT.
Tip 10397:	How to disable switching drawings when hovering on the DWG tab thumbnail?
Tip 9807:	Automatic elevation labels.
Tip 9739:	Size of a saved DWG file grows unexpectedly.
Tip 9685:	DWG thumbnail is not displayed with some files. Why?

Selected tip: How to make some layers an "inactive backgound image"?

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