What is a DWG file?

A DWG file is a drawing saved in AutoCAD's native binary format, and it is the most common way 2D and 3D CAD drawings are stored and exchanged. The name is short for "drawing". You can open a .dwg file without AutoCAD: drop it into the viewer on this page and it renders in your browser, with nothing uploaded.

DWG format: what is inside a .dwg file

The DWG file format is a binary container for everything a drawing needs: geometry, layers, text styles, dimension styles, block definitions, layouts and plot settings. Architects, civil and structural engineers, MEP designers, surveyors, machine shops and GIS teams all use it, because AutoCAD and most other CAD programs read it directly.

Internally a DWG has three parts. The header starts with a six-character version string (for example AC1032) followed by drawing variables such as units, limits and the current layer. A set of sections holds the symbol tables (layers, linetypes, text styles, blocks), the class definitions, the object map and a preview thumbnail. The entities are the drawing itself: lines, polylines, arcs, circles, text, hatches, dimensions, block references and 3D solids, each stored as a compact object with a unique handle. From AutoCAD 2004 on, the sections are also compressed and paged, which is why a DWG is usually several times smaller than the same drawing saved as DXF.

The specification is owned by Autodesk and is not published. Other programs read DWG through reverse-engineered libraries: the Open Design Alliance's Teigha/ODA SDK (used by BricsCAD, Bentley and many others) and the open-source LibreDWG (used by this viewer). "TrustedDWG" or "true DWG" is Autodesk's label for a file last saved by an Autodesk product; a file saved by other software is still a normal DWG, AutoCAD just shows a notice when it opens it.

DWG file versions

The DWG format changes roughly every three AutoCAD releases. The version code is the first six bytes of the file. A newer AutoCAD opens every older version; an older AutoCAD cannot open a newer one, which is the usual reason a drawing "is not valid" on a colleague's machine.

The full list back to AutoCAD 1.2, how to read the code from a file, and how to save a drawing down to an older version are on the DWG versions page. This viewer opens AC1014 through AC1032 (R14 to 2018+); R12 and older files are not supported.

How to open a DWG file

You do not need AutoCAD to look at a drawing. The options, from lightest to heaviest:

• This viewer. Drop the .dwg on the page. The file is converted to DXF on your device with LibreDWG compiled to WebAssembly, then drawn with a WebGL renderer. You get pan, zoom, fit to view, a layers panel, a distance measure tool, printing and PNG/SVG/PDF export. Nothing is uploaded; closing the tab removes the file. It works in Chrome, Edge, Firefox and Safari on Windows, macOS, Linux and ChromeOS. A typical 1–20 MB drawing opens in 1–10 seconds on a laptop; the first file in a session also downloads a 9 MB WebAssembly module once.
• Autodesk DWG TrueView (Windows, free install) renders with AutoCAD's own engine and plots with CTB plot styles.
• Autodesk Viewer online opens DWG after you upload it to an Autodesk account.
• LibreCAD, QCAD, FreeCAD, BricsCAD Shape for viewing plus editing on the desktop.

Step-by-step instructions for each platform are in how to open a DWG file, how to open a DWG file without AutoCAD and how to open DWG on a Mac.

How to convert a DWG file

Most "DWG to something" requests are really "I need to share this with someone who does not have CAD". For that, export from the viewer: DWG to PDF gives a vector PDF on an A-series page, DWG to SVG gives a vector file for Illustrator or a browser, and DWG to PNG gives a raster image of the current view. Layers are flattened in all three, because PDF, SVG and PNG have no CAD layer concept.

To exchange with other CAD programs, convert DWG to DXF. This viewer converts DWG to DXF on the device in order to render it, but it does not offer a DXF download yet; use Autodesk DWG TrueView or the free ODA File Converter for a DXF file.

The reverse direction, PDF to DWG, is a different problem. A vector PDF can be imported as lines and text by AutoCAD's PDFIMPORT command or by converters built on the same idea; a scanned PDF has no vectors and must be traced. No browser viewer, including this one, writes DWG files.

DWG vs DXF, DWF and other CAD formats

DWG is the working file. DXF is Autodesk's documented text version of the same data, made for exchange with other programs and CNC machines. DWF is a published, read-only package for review, closer to a PDF than to a drawing. For the full comparison see DXF vs DWG and DWF vs DWG, and for the wider family of formats see what is a CAD file.

Frequently asked questions