What is the difference between 4,6,7, and 8 digit SIC codes?
Governed reference
Authority & Trust HubThe Standard Industrial Classification (SIC) system is a framework established by the U.S. government to categorize business establishments by their primary economic activity. At its core are 4-digit SIC codes, which define the official industry meaning layer used for historical continuity and legacy compatibility.
Over time, some datasets have introduced additional digits (6–8) to support finer segmentation. These additional digits are commercial extensions built on top of the official framework and should be interpreted as dataset-specific layers, not government standards.
Public access & services boundary: SICCODE.com has always maintained free public access to core SIC and NAICS classification reference materials; paid services support organizations that require formal verification, documentation, enterprise-scale classification, or application of classification data to internal business records.
For foundational context, see What is a SIC Code.
The Role of 4- and 6-Digit SIC Codes
SICCODE.com presents both 4-digit and 6-digit SIC representations to help users work across historical records and modern datasets. The key distinction is the meaning layer.
- 4-Digit SIC (official standard): Defines the industry itself and is the authoritative layer for interpretation and continuity.
- 6-Digit SIC (commercial extension): A dataset-defined subdivision of a 4-digit industry used to add analytical or targeting detail. These extensions vary by source and must be documented.
Extended Codes: 7- and 8-Digit SIC Codes
Some private data providers further extend SIC to 7–8 digits. These are not inherently “more correct” than 6-digit variants; they are simply alternative segmentation schemes designed for internal analysis, marketing, or modeling.
Best practice is to treat all SIC digits beyond four as extensions and always retain the underlying 4-digit SIC to preserve defensible meaning.
Strategic Applications
When used correctly, SIC classifications can support:
- Targeted analysis: Grouping establishments consistently within a defined industry scope.
- Longitudinal research: Preserving comparability across older datasets and reporting systems.
Integrating SIC and NAICS Codes
Many organizations maintain both SIC and NAICS fields to bridge historical continuity with modern reporting requirements. Use the official layer of each system (SIC 4-digit; NAICS 6-digit) as the base meaning, then document any extensions or mappings.
Reference tools: SIC Code Directory · NAICS Code Directory
Interpretation rule: Use the official SIC industry (4-digit) to define what a business is. Treat 6–8 digit SIC values as optional, documented extensions that describe how a dataset chooses to segment that industry.
- Are 6-digit SIC codes official?
No. Official SIC industries are defined at four digits. Six-digit values are commercial extensions used by datasets. - Are 7- and 8-digit SIC codes more accurate?
Not necessarily. They reflect different segmentation choices, not a higher government standard. - What should I store in my system?
Store the 4-digit SIC for meaning and continuity, and store any extended digits with a short note explaining how they were derived.