DWG file - All about the DWG file format

DWG (short for drawing) is the native file format of the AutoCAD CAD program. It is used for 2D and 3D designs. The format developed by Autodesk is proprietary. The specifications are therefore not public and other programs can only use it to a very limited extent, if at all. Nevertheless, due to the high distribution of AutoCAD, the DWG file format has a great importance for the exchange of CAD designs. The program DWG TrueView, which is also offered by Autodesk, makes it possible to view DWG files even on computers without AutoCAD. Editing of the DWG files is not possible with DWG TrueView.

Typical application of DWG files

Just like other CAD formats, for example DXF, DGN or the ISO-standardized STEP, the DWG format is used to digitally store blueprints for machines and other constructions. The format supports the arrangement of objects in a three-dimensional coordinate system. Thus, it is possible to create not only 2D construction plans, but also 3D renderings of the planned objects. The format is thus also suitable for developing complex plans for the construction of multi-part buildings. In addition, single-part objects can be planned, which can then be realized with a 3D printer, for example. In architecture, CAD designs and thus the DWG format are also used. Both in the planning of entire buildings and in the digital preparation of interiors, the use of DWG files can play a role.

Especially in the professional environment, for example in engineering, in architectural offices or in the design of medical products (e.g. prostheses), the format is used. Due to the complex operation and high pricing, AutoCAD hardly plays a role in the private sector. Thus, the DWG format is also of little importance for private users. Formats such as STL are much more popular among owners of small 3D printers used at home.

Structure of the DWG format

DWG designs can contain 2D and 3D CAD blueprints. The actual designs are stored in a comparatively compact binary format that Autodesk does not communicate externally. Nevertheless, thanks to the reverse engineering efforts of the developers of the Open Design Alliance, parts of the DWG format are public. 

Object data in the DWG format is generally stored separately from the actual map. This map records where exactly the objects are placed in the coordinate system. In addition to graphical entities, such as fixed geometric shapes (circle, square, freehand polygon, etc.), non-graphical entities (e.g. settings) are also stored as objects. Relationships and dependencies existing between objects are also stored as objects. This results in meta-objects that can be reused. The actual map part of the design thus ultimately stores only the positions of the elements.

In addition, each DWG file contains a header stored in plain text at the beginning of the file. This header contains meta data such as the version of the DWG format used, the units of measurement used in the design and information about the time when the file was last edited. In addition, the header is stored a second time at the end of the file. This is primarily a relic of the days when tape drives were used on a daily basis. Today, redundant, double storage of meta information is still relevant at best for integrity assurance reasons.

History of the DWG file

The origins of the DWG file go back to the late 1970s. It was originally developed at that time for a CAD program called Interact. In 1982, Autodesk adopted the format with the release of AutoCAD 1.0. Since then, there have been a total of 20 newer versions of the format, each supporting innovative features of the current AutoCAD version. Current AutoCAD versions are basically able to read older DWG files and convert them to the latest version of the format. However, due to the more than 40-year history of the file format, compatibility problems may occur with some very old DWG versions. In practice, however, this hardly matters.

FAQ about DWG file format

What is a DWG file?

DWG is the native file format of AutoCAD. It is used for 2D and 3D designs. The file format is vendor-specific for programs from the developer Autodesk. Other programs can only use it in an extremely limited way, if at all. However, since AutoCAD is widely used in the industry, the DWG format still has enormous importance for the exchange of CAD files and designs.

How can I open DWG files?

DWG files can be opened primarily with AutoCAD and the DWG TrueView tool also developed by Autodesk. Some other CAD programs like IntelliCAD or BricsCAD also support the format. However, due to the proprietary nature of the file format, these programs often cannot use all the current features.

How can I convert a DWG file to PDF?

In order to export DWG CAD designs to PDF format with AutoCAD, it is enough to open the AutoCAD main menu and select the "Export" menu item there. After that, a menu appears from which a number of other CAD formats can be selected in addition to PDF format. After the selection, a storage location can be specified. The export of the PDF file then takes place automatically. Conversely, however, AutoCAD cannot re-read rendered construction plans in PDF format and convert them to CAD designs.

Is DWG TrueView free of charge?

Yes, DWG TrueView is offered by Autodesk free of charge. The program is primarily for viewing DWG files on computers that do not have AutoCAD installed. In addition, with DWG TrueView it is possible to convert older files of the format to a newer version.

What is the difference between DWG and DXF?

The DXF format (Drawing Exchange Format) is also developed by Autodesk and is primarily used to exchange files between different CAD programs. Basically, DXF supports 3D coordinates just like DWG, but today it plays a role primarily as a format for storing and exchanging 2D designs. Unlike DWG, in the case of DXF, Autodesk publishes the format specifications so that developers of other CAD solutions can fully implement it. The open nature of the DXF format also makes it easy to manipulate the files with your own scripts and, for example, perform calculations with the dimensions used in the file.