Converting DWG to OBJ and Turning CAD Data into 3D: A Step-by-Step Guide for Engineers

Table of Contents

• What are DWG and OBJ? – First, we explain the basics of the DWG format and the OBJ format

• Benefits of converting DWG to OBJ – Explains the purposes and advantages of turning CAD data into 3D

• DWG to OBJ conversion procedure [Step-by-step] – Guides the actual conversion method step by step

• Precautions and troubleshooting during conversion – Points to watch and methods for dealing with problems during conversion work

• Summary: Possibilities opened by 3D conversion – A summary of the article and suggestions for further applications

• FAQ – A collection of frequently asked questions and their answers

What are DWG and OBJ?

DWG (drawing) is a file format for design data widely used in CAD software. DWG files can store a wide range of geometric information with high precision, from 2D drawings such as architectural plans and machine part designs to 3D geometry such as solid and surface models. It is a standard format for designers and engineers, and because it also includes metadata such as dimensions and layer information, it is often used when exchanging drawings between CAD programs.

On the other hand, OBJ (object) files are a general-purpose file format that stores shape data for 3D models. Officially, it is the "Wavefront .OBJ" format established by Wavefront Inc., and it is mainly used as a standard in the 3DCG field. OBJ files record object shapes as polygon meshes (vertex coordinates and face composition), and, when necessary, materials and texture coordinates (described in .MTL files) may also accompany them. However, OBJ is a format specialized for pure shape data and does not include CAD-specific parametric dimension information, annotations, layer structures, or the like. In other words, it is helpful to remember that OBJ is a polygon mesh format, DWG is a CAD data format.

Benefits of Converting DWG to OBJ

So, why is it necessary to convert CAD DWG data into 3D models in OBJ format? For engineers, there are several benefits to consider.

• Can be used in 3D viewers and other software: DWG files may require dedicated CAD software to open, but if you convert them to OBJ, many free 3D viewers and general-purpose 3D applications can open and view the model. For example, even if project stakeholders do not have major CAD software, they can check and review the design model with another 3D tool if it’s in OBJ format.

• Usable in AR/VR and game engines: OBJ is widely supported by game engines and AR/VR platforms. Converting DWG design data to OBJ enables new uses for CAD data, such as walking through architectural models in VR or displaying machine part models at full scale in AR.

• Supports 3D printing and CG rendering: OBJ, like STL, is a polygon model format, so it can be handled by slicer software for 3D printers and by CG rendering software. If you convert 3D shapes created in DWG to OBJ, you can smoothly transition to processes such as 3D printing prototype parts or rendering product designs as photorealistic CG images.

• Data sharing and archiving: OBJ is one of the software-independent open formats. For long-term preservation and when sharing with external parties, converting proprietary DWG files to the more compatible OBJ format provides greater assurance than keeping them as DWG. For example, if you store completed design 3D data as OBJ so it can be referenced in the future, it can be viewed even without access to a specific version of CAD software.

In this way, converting DWG to OBJ dramatically increases the usability of 3D data. For designers, this can be regarded as an important step toward effectively leveraging models beyond the confines of CAD.

Step-by-step procedure for converting DWG to OBJ

Now, I will explain specifically how to convert DWG files to OBJ files. Here, I will introduce several common procedures. Please choose the method that best suits your environment and budget.

Method 1: Convert using CAD software

If you have CAD software that can handle the DWG format, using that software is the most reliable method. Below, using major CAD programs as examples, we outline the steps for converting to the OBJ format.

• Open the DWG file: In your CAD software, open the DWG file you want to convert. If the DWG contains a 3D model, the model space will display the solid geometry; if it only contains 2D drawings, it will remain a collection of lines with no thickness (※ see the precautions for 2D drawings described below).

• Mesh 3D solids (if necessary): If you have a 3D solid model, it will be meshed on export as is, but if you want to check or adjust the meshing beforehand, you can convert the solid into a mesh object using the `MESH` command or similar. For models that include curved surfaces, it's a good idea to set the mesh density (polygon count). If the polygons are coarse, shape accuracy will suffer — for example, cylinders may appear faceted — so adjust the subdivision level before export.

• Export (output to STL format): Unfortunately, because the standard features do not allow saving directly to OBJ, first export to STL as an intermediate format. From the menu bar select [File] > [Export], choose "Stereo Lithography (*.stl)" as the file type, and save. If the save dialog does not appear, you can also run the `EXPORT` command at the command line and select STL in the "File format" option. During export you may be prompted about units and resolution. To preserve the model's actual dimensions, specify the STL units to match the units used in the DWG (mm (in) or inch, etc.). Also, if a setting for surface detail (an angle tolerance such as "10 degrees") is requested, press Enter to proceed if the default value is acceptable (or choose a smaller value to create finer subdivision if needed).

• Convert the STL file to OBJ using a conversion tool: Next, convert the STL file you created into OBJ format. If you are on Windows 10 or later, using the built-in app 3D Builder (a 3D model editing app provided by Microsoft) is an easy method. Launch 3D Builder, select [Load] from the menu, and open the STL file you exported earlier. Once the model displays correctly, choose [Save] or [Save As] from the menu, select "OBJ (.obj)" from the list of file formats, and save. This will output the DWG-derived model in OBJ format. Using 3D Builder makes it convenient to perform a one-click STL→OBJ conversion without any complicated settings.

• Check the OBJ data: Open the exported OBJ file once in a viewer or similar and confirm that the geometry has been converted correctly. Check whether meshes are missing or the scale is incorrect. If necessary, adjust the model in the CAD software and export it again, or review the settings used when importing the OBJ. If there are no problems, the conversion is complete!

Method 2: Convert online without CAD software

Even if you don't have software on hand, you can use online conversion services to convert DWG to OBJ. There are several sites on the Internet that will automatically convert CAD files to other formats when you upload them via your browser. The typical usage is as follows.

• Choose an online conversion service: Use a web search for terms like "DWG OBJ conversion online" and select a converter site that appears trustworthy. Among well-known options are free services specialized in CAD/BIM data conversion. Because supported formats differ between services, confirm that the site supports "DWG input → OBJ output".

• Upload your DWG file: On the website, use the "Choose File" button or the drag-and-drop area to select and upload your DWG file. In some cases, you may need to enter your email address or agree to the terms of service. Also pay attention to the file size limit (large files may take a long time to upload or cause errors).

• Set the output format to OBJ and run the conversion: After uploading, if an output format option is available select OBJ and click the "Start Conversion" button. The conversion will be processed on the server side, and when it completes a download link will be displayed or a notification will be sent to the specified email address. Conversion often takes a few seconds to several dozen seconds.

• OBJファイルのダウンロード: Download the generated OBJ file (and any associated MTL files and textures, if present) following the instructions. Unzip or extract the downloaded files into an appropriate folder and check their contents. Note that some online services impose restrictions, such as temporary download links being valid only for a limited time (e.g., within 24 hours).

• Model check: Open the OBJ data obtained from the online conversion in a viewer or similar tool and verify that the geometry looks correct. In particular, CAD-specific curved surfaces can become triangular polygons and appear coarse (due to the mesh resolution of the automatic conversion). If there are problems, consider adjusting the conversion service's settings if possible, or trying a different service.

Online conversion is convenient because it requires no software, but you should be cautious about uploading confidential data. For items that cannot be sent outside the company, such as corporate drawing data, don't entrust them to online services; consider the following offline methods.

Method 3: Convert using free software

If you don't have CAD software on hand and can't upload files online, there are methods that make use of free software. There are few completely free programs that can open DWG files directly, but with some adjustments to the procedure it is possible to convert them.

• Convert DWG to an intermediate format: Open-source software often cannot read DWG files directly. Therefore, first convert the DWG to an intermediate CAD exchange format. If you can ask the provider of the DWG file, have them export it in formats such as DXF (for 2D drawings) or STEP/IGES (for 3D models).

• Load into CAD: Install a free 3D CAD application, then launch it and open the DXF or STEP files you prepared above. If the drawing is 2D, you can view the DXF geometry in the Draft workbench. If it is a 3D shape, the STEP solid should be loaded in the Part workbench or a similar workbench.

• Convert to mesh data (if necessary): If you are handling solid shapes in CAD, you must convert them to polygon meshes before exporting to OBJ. Select the relevant object and switch to the Mesh Design workbench, then use the "Convert to mesh" function to triangulate it. If a mesh density setting dialog appears, specify an approximate polygon count (smaller values produce finer detail but increase file size).

• Export as OBJ: With the meshed object selected, execute [File] > [Export] from the menu bar, specify the file format as "Wavefront OBJ (*.obj)" and save. In CAD, OBJ is included in the list of export formats by default, so you can export it simply by selecting it. Along with the OBJ file saved here, if material information exists an MTL file will also be exported to the same folder.

• Verify the results: Open the exported OBJ file in other viewers or 3D software to check. If the shape is as expected, the conversion was successful. By using CAD, even though it is via an intermediate format, everything can be completed offline, so you can convert with confidence.

The above are the typical methods for converting DWG to OBJ. Choose the procedure that best fits your software environment. Each has its own advantages and disadvantages, so let’s review the precautions to take during conversion in the next chapter.

Notes and Troubleshooting During Conversion

There are several points to note when converting DWG to OBJ. To ensure a smooth 3D conversion, make sure you understand the following items in advance.

• 2D drawings have no thickness: If a DWG file contains only a plan view (2D), converting it directly to OBJ will only place lines and curves in 3D space and will not produce a volumetric solid. For example, converting an architectural floor plan to OBJ yields line data with zero thickness for walls and floors. If you want to convert a 2D drawing into 3D, you need to create a solid model in CAD software by performing extrusion or solid-modeling operations. Note that simply converting the file format will not automatically create a 3D shape.

• Check units and scale: The OBJ format itself does not contain information about drawing units (mm or inch). Therefore, you need to adjust the scale when importing the OBJ according to the unit system used by the original DWG. For example, if a model in the DWG had 1 unit = 1 mm (0.04 in) and is converted to OBJ, another software might interpret it as "1 unit = 1 m (3.3 ft)" when importing, resulting in it being displayed 1,000 times larger. As a countermeasure, check the model's dimensions before and after conversion, and if necessary apply scaling or unit settings.

• Be mindful of polygon counts for complex solids: When you mesh a CAD solid model, depending on the geometry it can become an OBJ composed of a very large number of polygons (triangular faces). Designs with complex curved surfaces or many fine details can result in a large file size after conversion and longer loading times. As needed, adjust the mesh density settings during export and output the file after reducing to an appropriate polygon count. Conversely, if the polygons are too coarse and the shape looks faceted, increase the subdivision settings and re-export.

• Information loss: OBJ records only pure geometry data, so DWG-specific information will not be converted. For example, dimensions and annotation text in drawings, layer structures, blocks (instances of parts) cannot be represented in OBJ and will be lost. Also, colors and materials are basically limited to simple per-mesh color assignments, and CAD rendering material settings are not faithfully carried over. If you need that information, save it beforehand as screenshots or PDF drawings, or reproduce it in 3DCG software after converting to OBJ.

• Differences in coordinate axes: CAD and 3DCG software may differ in their model's coordinate systems and axis orientations. By default, the XY plane is horizontal (the plane of the plan view) and the Z axis is vertical, but when opening an OBJ the model may be flipped upside down or its orientation may be off. This is because many 3D tools use the Y axis as the vertical axis. As a workaround, use the axis conversion options when importing an OBJ, or rotate/flip the model to adjust it to the correct orientation.

• Handling conversion errors: Rarely, errors or issues can occur during the conversion process from DWG. If an online service fails, try reducing the file size or using a different service. If your software cannot export properly, saving the DWG once in an older version format and then re-exporting it may improve the result. Also, to isolate the problem, it can be effective to try converting only some elements as a test (you can confirm whether a specific object is the cause).

If you work with the above points in mind, you'll encounter far fewer problems when converting DWG to OBJ. Finally, let's summarize what we've covered.

Summary: Possibilities Expanded by 3D Conversion

Converting DWG drawings to OBJ files enables 3D conversion of CAD data. This is more than a mere file conversion; it brings significant benefits to engineers. The converted OBJ models can be displayed in 3D even in environments without specialized software, making it easy to share design intent. In addition, the range of uses for design data expands dramatically—covering simulations and presentations in virtual spaces and applications to physical prototyping. The procedure itself may feel somewhat laborious, but, as introduced in this article, it can be overcome with the right tools and ingenuity.

Furthermore, not only converting desk-based design data into 3D, but also acquiring real-world information as 3D data will become increasingly important. For example, if you can easily measure on-site dimensions and terrain and reflect them in 3D models, it helps bridge the gap between design and construction. For such uses, we recommend simple surveying using "LRTK", which combines a smartphone with a small positioning device. LRTK is an easy-to-use surveying tool that can be used without specialized knowledge, and while photographing with a smartphone it can record position coordinates with cm level accuracy (half-inch accuracy). By combining 3D models from CAD data with measured data acquired by LRTK, advanced project management that integrates the digital and the real becomes possible. If you are interested, please try using LRTK. It will surely reveal new possibilities for design work.

FAQ

Q: Can I convert a DWG to OBJ without CAD software? A: Yes, it's possible. Using an online converter like the one introduced in Method 2, you can convert DWG to OBJ without installing software. However, be careful with highly confidential data. If you want to do it offline, you can combine free software such as CAD with intermediate formats (DXF or STEP). It takes a few more steps, but with some ingenuity you can convert files even without CAD software.

Q: Can a 2D DWG drawing alone be converted into a 3D model? A: Simply converting the file format is not enough. If the DWG contains only 2D information such as plans, converting it to OBJ will still produce data with lines arranged on a plane. To create a 3D solid model you need modeling work in CAD software, such as extruding walls and columns to give them thickness. If you want to generate solids from 2D drawings, model them in CAD or other 3D-capable CAD software and then export to OBJ.

Q: When I open the converted OBJ, the size doesn't seem to be correct. What should I do? A: The cause may be a mismatch in unit systems. OBJ files do not contain unit information, so the importing software may interpret the scale incorrectly. As countermeasures, you can adjust the scale value when importing the OBJ, or standardize the original DWG to the metric system before converting it. For example, if "the model is displayed 1000 times larger," setting the import scale to 0.001 will result in the correct size. Check the unit and scale settings in each software's import options.

Q: What happens to CAD layer separation and dimension lines when converting to OBJ? A: Basically, that information is lost. OBJ is a format that records shape (polygon geometry), so layer divisions, dimensioning, annotation text, and similar information in CAD data are not carried over. If you want objects separated by layer, you must either export each layer separately before conversion or regroup objects in 3D software after OBJ export. In addition, dimension lines, hatches, and the like should be shared separately as drawings when necessary.

Q: Which software should I use to open the converted OBJ file? A: The easiest option is to use a 3D viewer or modeling software. On Windows, the "3D Viewer" app (previously named with an alternate transliteration) comes preinstalled, and you can display an OBJ by double-clicking it. You can also import it into free software to view it, or use a cloud-based 3D preview service to view it in your browser. Choose OBJ-compatible software according to your needs and open the file.