Convert DWG to STL

First: does your DWG contain a 3D object at all?

This is the question to settle before looking for a converter, because most DWG files are 2D drawings — plans, elevations, sections — made of lines, arcs and text. A 2D drawing has no volume, and no tool can turn one into an STL, because there is nothing to make solid.

Open it and orbit the view. If it stays flat from every angle, it is a 2D drawing. What you have is a shape you could extrude to a chosen thickness, which is a modelling job rather than a conversion, and one this site can help with: export the drawing as DXF or SVG, and an extrusion into STL is a real conversion we do.

If it does contain a 3D solid — AutoCAD does model in 3D, and so do Civil 3D and Advance Steel — then the export below applies.

Why there is no free DWG reader

Autodesk has never published the DWG specification. The format changes every few releases, and the only complete implementation outside Autodesk is the Open Design Alliance’s libraries, which are licensed commercially — membership costs thousands of dollars a year and the terms do not allow redistributing the capability in a free tool.

There is a reverse-engineered open library, LibreDWG, but it is incomplete, licensed under the GPL in a way that constrains how it can be used, and has no practical browser build.

This is why the keyword difficulty for DWG conversions looks so inviting and delivers so little: nobody is serving these searches for free because nobody legally can. It is the clearest example on this site of a low difficulty score meaning an impossible task rather than an open market.

DXF is the way around it. Autodesk publishes the DXF specification precisely so that other software can exchange drawings with AutoCAD, and every program that writes DWG also writes DXF from the same menu.

The three routes that work

From AutoCAD itself, if the drawing has a 3D solid: use the STLOUT command. Type STLOUT, select the solid, confirm, and choose a filename. The solid must be a genuine 3D solid — AutoCAD refuses surfaces and meshes — and it must sit entirely in positive coordinates, which is an old restriction that still catches people. Move the object above the origin if STLOUT complains.

Through a free CAD program: FreeCAD imports DWG if you install the ODA File Converter alongside it, which is free to download and use. Simpler still, ask for a DXF instead — FreeCAD reads DXF natively, and so does LibreCAD, QCAD and Fusion 360.

Through Fusion 360, which is free for personal use and imports DWG directly. It will also do the extrusion if what you have is a 2D drawing, which is frequently the real requirement.

In every case the shortest path is to ask whoever sent the DWG for a different format. A STEP file if it is 3D, a DXF if it is 2D. Both take them seconds and both open in free software.