What is the DGN file format?
.dgn (short for "design") is a file format used by Computer Aided Design (CAD) software, most notably Bentley Systems MicroStation. .dgn files store 2D and 3D project data - geometry, annotations, levels, models, and reference attachments - in a single design document. The format is typically used in architectural and construction-related projects, such as road, bridge, power plant, or shipyard development.
Two versions of the DGN format
The older version was based on Intergraph Standard File Formats (ISFF), originating from the Intergraph Interactive Graphics Design System (IGDS) of the early 1980s. This generation is sometimes called V7 DGN or Intergraph DGN, and its files use a fixed-record binary structure. The newer version, introduced by Bentley Systems in 2000, no longer conforms to the ISFF specification and is designated as V8 DGN. V8 files are wrapped in a Microsoft OLE2 Compound File Binary (CFB) container - the same low-level structure found in legacy .DOC and .XLS documents - and add support for unlimited design planes, 64-bit coordinate precision, and multiple named models within a single file.
.dgn files interoperate with .DWG and can be exported to .DXF for use in Autodesk products. Shared resources such as level definitions and text styles reside in .dgnlib library files, while reusable symbol elements are stored in .cel cell libraries.
Security & safety
RISK: LOWA DGN is passive CAD design data - geometry, levels and references - with no executable code, so opening one in a viewer is safe. The realistic cautions are non-malware: V7 vs V8 format differences (an old V7 DGN may need MicroStation to upgrade), and DGN<->DWG translation quirks where levels/layers, cells/blocks and custom line styles don't map perfectly - always check a converted drawing before relying on it. Treat shared engineering drawings as confidential intellectual property and get files from sources you trust. (Be mildly cautious that the V8 DGN's OLE2 compound-file container is the same wrapper as legacy macro-bearing Office files, but DGN itself does not carry Office macros.)
Format details
in a nutshellPrograms that open DGN files
Windows4 apps
Bentley View
Free Bentley's free viewer for DGN/DWG/DXF and 50+ formats. Double-click a .dgn or File > Open to view, measure and print read-only. The primary free DGN opener.
Bentley MicroStation
Paid The native editor. File > Open the .dgn to view and fully edit elements, levels, models and references.
Autodesk AutoCAD
Paid Import a DGN (DGNIMPORT) or attach it as an underlay (DGNATTACH); also used to convert DGN to DWG. Paid CAD.
ODA Drawings Explorer
Free Free Open Design Alliance viewer that opens DGN and DWG; view and inspect without MicroStation. 
macOS2 apps
ODA Drawings Explorer
Free Free cross-platform viewer; open the .dgn to view (MicroStation/Bentley View are Windows-only).
TurboCAD (TurboCAD Mac)
Paid Imports DGN for viewing/editing on macOS. Paid CAD; verify DGN import in your edition. 
Linux1 app
ShareCAD / online CAD viewers
Free Upload the .dgn in a browser to view it without installing anything. Avoid uploading confidential drawings. Technical details
deep spec| Format generations | V7 DGN (ISFF-based, pre-2000) and V8 DGN (OLE2/CFB container, 2000 onward) |
| V7 file signature | Bytes 08 09 FE FF at offset 0; flat fixed-record element stream (Intergraph IGDS heritage) |
| V8 file signature | OLE2 Compound File Binary header D0 CF 11 E0 A1 B1 1A E1 at offset 0; internal streams identified by .dgn extension context |
| MIME type | image/vnd.dgn (IANA registered); application/octet-stream as generic fallback |
| Coordinate precision | 64-bit double-precision floating point in V8 DGN; 32-bit fixed-point UOR (Units of Resolution) in V7 |
| Geometry types | 2D/3D lines, line strings, arcs, ellipses, B-splines, surfaces, meshes, and SmartSolids (ACIS-kernel solids) |
| Design organization | Levels (layer equivalent), named models, and reference file attachments all contained within one .dgn file |
| Design units | User-configurable master units and sub-units; supports imperial (feet/inches) and metric (meters/mm) in the same file |
| Companion file types | .dgnlib for shared level definitions, line styles, and text styles; .cel for reusable cell (symbol) libraries |
| Interoperability | Native read/write of .dwg (AutoCAD format); export targets include .dxf, PDF, SVG, IFC, and Bentley i-model |
| Color model | V7: indexed 256-color table per design file; V8: color books with full RGB and RGBA support |
| Text encoding | V8 supports Unicode (UTF-16LE) for multilingual annotation text; V7 uses 8-bit legacy character encodings |
| Primary authoring software | Bentley MicroStation; Bentley View provides free read-only access; AutoCAD reads .dgn via built-in translation |
| Sector use | Infrastructure, transportation, utilities, architecture, and shipbuilding - especially government and large-scale civil engineering workflows |
| Released | Intergraph IGDS, early 1980s; Bentley MicroStation since 1985; V8 DGN format since 2000 |
| Specification | www.bentley.com |
DGN conversions
Community Q&A
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