What is the Difference Between 4, 6, 7 and 8-digit SIC Codes?
Official U.S. SIC codes are defined at the 4-digit level Official. When you see 6-, 7-, or 8-digit SIC-style codes, they are typically vendor-defined extensions used to add marketing or analytical granularity Extended—not part of the official government SIC standard.
4-Digit SIC Codes Official
Standard Industrial Classification (SIC) codes are four-digit numerical identifiers originally developed for consistent economic reporting and comparability across agencies and datasets. The official SIC structure is standardized at the four-digit level.
6–8 Digit Extended SIC Codes Extended
“Extended SIC” (6-, 7-, or 8-digit) codes are commonly found in commercial tools and private databases. They are not maintained as an official government standard. Instead, they are proprietary subdivisions built on top of four-digit SIC industries to support finer segmentation.
Governance note: 6-, 7-, and 8-digit SIC codes are non-standard extensions. They can be useful for marketing granularity and internal analytics, but they are not part of the official U.S. SIC standard. When accuracy, auditability, or cross-dataset comparability matters, treat the 4-digit SIC as the authoritative anchor and document the specific vendor definition used for any extension.
How the Digits “Nest” (4 vs 6 vs 7 vs 8)
A helpful way to think about extended SIC codes is that they start with an official 4-digit SIC, then append additional digits to create more granular subcategories. The added digits are not standardized across the market.
| Code Length | What It Represents | Standardized? | Typical Use |
|---|---|---|---|
| 4-digit | Official SIC industry classification | Yes (Official) | Reporting consistency, legacy datasets, longitudinal analysis, reference lookups |
| 6-digit | Vendor-defined subdivision of a 4-digit SIC industry | No (Vendor-defined) | Marketing segmentation, list building, internal analytics |
| 7-digit | Additional refinement layer (provider-specific) | No (Vendor-defined) | More precise targeting and categorization in private datasets |
| 8-digit | Highly granular extension (provider-specific) | No (Vendor-defined) | Narrow niche classification, campaign targeting, specialized research workflows |
Note: Extended structures differ by provider. Two databases may use the same 4-digit SIC but define different 6–8 digit extensions.
Expansion Example: One Official SIC → Multiple Extended Options
The table below illustrates the idea of “expansion.” The 4-digit SIC stays constant while extensions branch into more specific segments. The exact labels and meanings of extended segments depend on the provider maintaining the taxonomy.
| Official 4-digit SIC | Example Extended 6-digit | Example Extended 7-digit | Example Extended 8-digit | Interpretation (provider-defined) |
|---|---|---|---|---|
| 1234 Official | 123401 Extended | 1234011 Extended | 12340112 Extended | Illustrative only: extension digits represent finer subdivisions defined by the taxonomy owner |
Practical Guidance: When to Use Which
Use 4-digit SIC when you need a standard anchor
- Comparability across datasets or time periods
- Legacy reporting and historical trend analysis
- Documentation for audit-ready classification decisions
Use extended SIC when granularity is the priority
- Marketing segmentation and targeted list building
- Internal categorization and workflow routing
- Specialized research where a provider’s taxonomy is consistently applied
Find SIC, Extended SIC, and NAICS Directories
For lookup and reference, use the directories below. When comparing datasets, note whether the source uses official four-digit SIC or a vendor-defined extended structure.