What is a .dwg file?
AutoCAD Drawing · 3D model · Autodesk · 1982
DWG is the native format of AutoCAD and the industry standard for 2D and 3D CAD drawings in architecture and engineering. It is a dense, proprietary format best opened in CAD software or a dedicated viewer.
What is a .dwg file used for?
DWG stores precise vector geometry, layers, dimensions and metadata for technical drawings and models. It is the working format of the CAD world.
The format is older than AutoCAD itself. Mike Riddle developed it for the Interact CAD package in the late 1970s, and Autodesk licensed the technology in 1982 to make it the native format of AutoCAD 1.0. It has never been published as an open specification, so every non-Autodesk program that reads DWG relies on the Open Design Alliance, a consortium founded in 1998 that maintains a reverse-engineered read and write library. That is why BricsCAD, DraftSight and the free ODA File Converter can handle DWG at all.
DWG is strictly version-specific, and this is the single most common reason a drawing will not open. Each generation writes a different internal format, and the version code sits in the first six bytes of the file as ASCII text: AC1015 is the DWG 2000 format (AutoCAD 2000 to 2002), AC1018 is DWG 2004 (2004 to 2006), AC1021 is DWG 2007 (2007 to 2009), AC1024 is DWG 2010 (2010 to 2012), AC1027 is DWG 2013 (2013 to 2017) and AC1032 is DWG 2018, still written by every release since. Open the file in a text editor and the first line reveals which one you have.
If an older program refuses a drawing, save it down rather than hunting for a converter: AutoCAD, BricsCAD and the free DWG TrueView all offer Save As with a target DWG version, and the free ODA File Converter batch-converts a whole folder between versions on Windows, macOS and Linux.
Several Autodesk extensions look like DWG and are not. DXF is the documented interchange format that carries the same geometry in a readable form, DWF is a compressed view-and-markup export that cannot be edited back into a drawing, DWT is a drawing template and DWS a standards file, while .bak and .sv$ are AutoCAD's backup and autosave copies that can be renamed to .dwg to recover work. For sharing a drawing with someone on different software, export DXF; for sending it to someone who only needs to look, export PDF.
What opens a .dwg file?
The .dwg format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- AutoCAD
- DWG TrueView (free)
- BricsCAD
- DraftSight
- ODA File Converter
macOS
- AutoCAD for Mac
- BricsCAD
- ODA File Converter
- LibreCAD (after converting to DXF)
Linux
- ODA File Converter
- BricsCAD for Linux
- LibreCAD (after converting to DXF)
iPhone and iPad
- AutoCAD mobile app
- DWG FastView
Android
- AutoCAD mobile app
- DWG FastView
Web
- Autodesk Viewer
- ShareCAD
Open a .dwg file step by step
- Confirm the file really is a .dwg. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with AutoCAD or DWG TrueView (free).
- On Mac, use AutoCAD for Mac or BricsCAD.
- On Linux, try ODA File Converter or BricsCAD for Linux.
- On an iPhone or iPad, use AutoCAD mobile app or DWG FastView.
- On Android, use AutoCAD mobile app or DWG FastView.
- Still stuck? Convert the .dwg to DXF, which opens more widely.
Why can't I open my .dwg file?
Almost always because no installed app understands DWG. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .dwg at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .dwg file
You can convert a .dwg file to DXF, PDF, SVG.
The free ODA File Converter turns DWG into DXF, which almost every CAD package reads. LibreCAD and QCAD then open the DXF. Custom object types from AutoCAD verticals do not survive the trip.
What is the .dwg file signature (magic bytes)?
A .dwg file starts with the hex bytes 41 43 31 30, which read as AC10 in ASCII. Programs identify DWG by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for DWG. For a full breakdown, see the AutoCAD DWG file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 41 43 31 30 | 0 | AC10 | 'AC10' version prefix (e.g. AC1027) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .dwg file?
DWG is the native format of AutoCAD and the industry standard for 2D and 3D CAD drawings in architecture and engineering. It is a dense, proprietary format best opened in CAD software or a dedicated viewer.
How do I open a DWG without AutoCAD?
Use Autodesk's free DWG TrueView to view, measure and print on Windows, or the free ODA File Converter on Windows, macOS and Linux to turn the drawing into DXF or an older DWG version. Autodesk Viewer opens a DWG in the browser with no install at all.
How do I convert a DWG to PDF?
Open the drawing in a CAD app or a free viewer like DWG TrueView and use its Plot or Print to PDF option. Online CAD viewers can also export a DWG to PDF without installing anything.
How do I open a DWG file on an iPhone or Android phone?
Install the AutoCAD mobile app or DWG FastView, both of which are free to view drawings, then open the file from Files, Drive or an email attachment. Both let you pan, zoom, measure and switch layers, though editing needs a subscription.
Why does my DWG say it is an unsupported or newer version?
Your program is older than the drawing. The first six bytes of the file name the format, for example AC1032 for DWG 2018 and AC1027 for DWG 2013. Ask the sender to Save As an older DWG version, or run the free ODA File Converter to convert it down yourself.
What is the difference between DWG and DXF?
DWG is Autodesk's compact native format and DXF is the documented interchange format Autodesk publishes so other software can read the same geometry. DXF files are larger, can be plain text, and lose some AutoCAD-specific objects, but they open in far more programs, including laser cutters and CNC software.
Is a DWF file the same as a DWG?
No. DWF is Autodesk's Design Web Format, a compressed snapshot for viewing and marking up a drawing. It is not editable CAD geometry, so you cannot turn a DWF back into a working DWG.
Related formats
Sources
Details on this page were checked against authoritative references. How sources are ranked and what is deliberately left out is set out in the methodology.