What Is a SIC Code? SIC Structure, Primary Code Rules & Extended SIC Segmentation

Updated: 2026
Reviewed By: SICCODE.com Industry Classification Review Team
Data Lineage: About Our Data Team

Governed reference

Authority & Trust Hub

SIC (Standard Industrial Classification) is a U.S. government-originated 4-digit industry coding system that categorizes businesses by their primary activity to support consistent reporting, analysis, and comparability across industries. SIC remains widely used for legacy reporting, market segmentation, and workflows where historical continuity matters. The U.S. government’s SIC maintenance ended in 1987; continued use today is primarily for legacy continuity and commercial data environments.

Defensible workflow: Use the directory to shortlist candidates, open the SIC code detail page to verify the official definition and included/excluded boundaries, then document the proxy used (commonly revenue) to support audit-ready classification. If you use extended segmentation, document it as a marketing-level layer separate from the official 4-digit SIC baseline.

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What SIC Is (And What It’s Not)

SIC is a legacy industry classification system designed to categorize businesses using a consistent, structured framework. It remains valuable because many datasets, filings, and historical reporting systems were built around SIC and still require it for comparability.

SIC is…

  • A standardized coding system centered on a 4-digit official baseline
  • Used for longitudinal comparability across legacy datasets and reporting
  • Commonly used for market segmentation, list building, and historical analysis

SIC is not…

  • A complete description of every business line at a company
  • A substitute for reading scope boundaries (included vs excluded)
  • The same system as NAICS (they classify industries differently)

When to use SIC vs NAICS: Use SIC when you need historical continuity, legacy dataset alignment, or workflows built around SIC. Use NAICS when you need the modern, process-based standard used across North America.

Compare systems: SIC Codes vs NAICS Codes • NAICS primer: What Is a NAICS Code? • Systems overview: Industry Classification Systems Overview • Documented government usage: What Government Agencies Still Use SIC Codes?

SIC Structure: Division to 4-Digit

SIC is hierarchical. The official classification is commonly treated as a 4-digit baseline used for consistency across reporting and analysis.

Division (Top Level)
→
Major Group (2-digit)
→
Industry Group (3-digit)
→
Industry (4-digit)

If you are doing official or baseline classification, treat 4 digits as the defensible anchor. Extended codes should be documented as a separate segmentation layer.

External reference (official manual): OSHA SIC Code Manual.

How to Read a SIC Code (Worked Example)

SIC codes read from general to specific. Use this pattern to understand what each level contributes.

Division

20–39 Manufacturing (range example)

Major Group (2)

25 Furniture & Fixtures

Industry Group (3)

251 Household Furniture

Industry (4)

2514 Metal Household Furniture

Extended (marketing)

SIC Code 2514-02 Furniture-Outdoor (Manufacturing)

Extended examples are commonly used for segmentation in commercial datasets; they are not the official government SIC endpoint.

NEC note (important for accuracy): The digit “9” sometimes appears in the 3rd or 4th position to designate “Not Elsewhere Classified (NEC).” These buckets are not always homogeneous—use them carefully and verify whether a more specific code fits.

Primary SIC Code and the “Dominant Activity” Rule

A primary SIC code represents the dominant business activity for the unit being classified (commonly the operating location or reporting unit in your dataset). Dominance is usually determined using a measurable proxy such as revenue, with other proxies used as tie-breakers when needed.

Example A (majority dominance): 51% primary activity, 49% combined secondary activities.

Primary 51% Secondary 49%

Example B (three-way split): primary can still be primary even at 40% if the other activities are 35% and 25%.

Primary 40% Other activities 60%

Best practice: document the proxy used (revenue, payroll, hours, headcount) and keep it consistent across time. If the mix changes materially, review the primary code.

Cross-system decision help: How to Choose the Correct NAICS or SIC Code.

Search vs. Classify (The Defensible Workflow)

Keyword search helps you find candidate SIC codes. Classification is the verification step that makes the selection defensible for audits, filings, analytics integrity, and list quality.

1) Start with an activity keyword
Describe what the unit primarily does (revenue-generating activity)
2) Shortlist candidates
Use lookup results to identify likely matches
3) Open the code detail page
Confirm the official definition + scope notes
4) Verify boundaries
Check included vs excluded activities
5) Document the decision
Record the proxy used (revenue, etc.)

In governance workflows, steps 3–4 are what separate “sounds right” from a defensible classification.

Risk Control: Boundaries and Common Misclassification Traps

Why boundary checks matter

SIC misclassification typically happens when a code name sounds right but fails the scope test. Boundary mistakes can distort benchmarking, segmentation, credit/underwriting grouping, and downstream reporting.

  • Verify included vs excluded activities to avoid near-match errors.
  • Prefer specific codes over NEC buckets when a clear match exists.
  • Keep a documented proxy so decisions are repeatable across time and teams.

Governance references: SIC Classification Methodology • SIC Data Governance & Versioning

Helpful SIC Tools and Reference Guidance

Find codes (lookup & directory)

Browse the SIC hierarchy or search by keyword to open a specific SIC code page for definition and boundaries.

SIC Code Directory & Lookup

Need help choosing between systems? How to Choose the Correct NAICS or SIC Code

Authority, accuracy, and governance

Use these references when you need consistency, defensibility, and organization-wide alignment.

SIC Classification & Reference Center
SIC Accuracy Benchmarks
SIC Data Governance & Versioning

Code conversion tools (cross-reference)

Extended (Marketing-Level) SIC Codes

The official SIC structure is anchored at 4 digits. However, many commercial datasets use extended SIC codes (often shown as 6-digit or hyphenated formats) to support finer segmentation for list building, niche targeting, and competitive analysis.

Important: Extended SIC codes are a commercial/marketing segmentation layer used to refine targeting beyond the official 4-digit SIC baseline.

Explore extended segmentation: Extended SIC Code Lookup Directory.

SIC History and Continuity Value

SIC remains important because it is deeply embedded in legacy systems, historical reporting, and longitudinal datasets. Many organizations maintain SIC-based comparability even after adopting NAICS for modern classification workflows.

Mobile tip: Scroll horizontally to view the full timeline.
Year Milestone Why it matters
1937 SIC established Created a consistent baseline for U.S. industry comparability
1987 Major revision cycle (final government update) Updated categories to reflect economic shifts while preserving continuity
1997 NAICS introduced Modernized classification (process-based) while SIC remained widely used in legacy systems
Present Continued usage in legacy and commercial contexts SIC persists in market data, segmentation, and many historical continuity workflows

External reference: OSHA SIC Code Manual. NAICS context: What Is a NAICS Code?.

GEO: Using SIC for Geographic Market Strategy

SIC is also a powerful GEO segmentation key when paired with location: it lets you quantify and target industries by geography (state, metro, county, ZIP, or custom territories) using a consistent industry baseline.

Territory planning

Build or refine territories by combining geography with a 4-digit baseline (and optional extended segmentation for precision).

Market sizing

Estimate how many businesses exist in an industry within a region before launching outreach.

Use the SIC baseline to identify the “Total Addressable Market” (TAM) within specific regions to prioritize sales resources.

Competitive density

Compare industry concentration across regions using the same SIC baseline for apples-to-apples analysis.

GEO accuracy depends on classification accuracy: If your SIC code is wrong, every geographic slice is distorted. Verify the definition and boundaries before using SIC in location-based analytics or targeting.

If you need industry + geography targeting, start with verified lists: USA Business Lists.

How SIC Is Used in Business and Government

Industry identification

Organize customers and prospects by industry to support segmentation, reporting, and analysis.

Start with lookup: SIC Code Directory & Lookup.

Marketing & segmentation

Use SIC (and optional extended SIC) to target niche markets, build competitive sets, and refine outreach.

Extended layer: Extended SIC Directory

Compliance & filings

SIC is used in several reporting and filing contexts where industry tags support sorting and comparability.

Compare systems: SIC vs NAICS

Common business use cases

  • List building and prospecting: classify and segment outreach lists by SIC. See: SIC Business Lists
  • Customer database enrichment: append SIC codes to customer records to unlock segmentation and analytics. See: SIC Code Append
  • Competitor analysis: identify peers within the same SIC baseline (and use extended segmentation for precision).
  • Historical benchmarking: align trend analysis across time using the consistent SIC baseline. See: SIC Accuracy Benchmarks

Common government and research use cases

  • Uniformity and comparability: consistent industry grouping for statistical analysis.
  • Data collection and analysis: supports structured reporting and industry-based research.
  • Legacy system continuity: many long-running programs and datasets still reference SIC.

FAQ

  • Does the official SIC system end at 4 digits?
    Yes. The official SIC baseline is a 4-digit industry code. Many commercial datasets add extended (marketing-level) detail, but that extended layer is separate from the official 4-digit SIC standard.
    Explore extended segmentation: Extended SIC Code Lookup Directory.
  • What is a primary SIC code?
    A primary SIC code represents the dominant business activity for the unit being classified, typically determined using a measurable proxy such as revenue. If your mix changes materially, review the primary code.
  • Why do “NEC” SIC categories matter?
    “Not Elsewhere Classified (NEC)” groupings can be broader and less homogeneous than specific codes. When possible, choose the most specific code that fits the definition and boundaries.
  • Should I use SIC or NAICS?
    Use SIC for legacy reporting and historical comparability; use NAICS for the modern, process-based standard. Many organizations maintain both for cross-dataset consistency.
    Help choosing: How to Choose the Correct NAICS or SIC Code.
  • How does SIC relate to ISIC for international comparisons?
    ISIC is a commonly used international industry classification framework. For international translation workflows, organizations typically use mapping tables to align local systems (like SIC or NAICS) to ISIC categories for cross-country comparability.
    ISIC lookup (reference): ISIC Code Lookup Directory.


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