What Are SIC Codes and NAICS Codes? A Complete Guide to Industry Classification

If you have ever worked with a business database, applied for a government contract, filed an SEC report, or researched an industry for market sizing, you have encountered industry classification codes. The two systems you will see most often are SIC codes (Standard Industrial Classification) and NAICS codes (North American Industry Classification System).

These codes are deceptively simple — a four or six-digit number assigned to every business in the United States based on what that business does. But understanding how they work, when to use each system, and how to navigate their structure unlocks powerful capabilities for sales targeting, market research, regulatory compliance, and competitive analysis.

This guide covers everything you need to know about both systems — their history, their structure, their differences, and exactly how to use them in practice.

1. What Is a SIC Code?

A SIC code (Standard Industrial Classification code) is a four-digit number that classifies a business by its primary economic activity. The system was developed by the US government in 1937 during the New Deal era, when federal agencies needed a standardized way to track economic activity across different industries during the recovery from the Great Depression.

The SIC system organizes all industries into 10 broad divisions (identified by letter ranges), which break down into 83 major groups (2-digit codes), then into 416 industry groups (3-digit codes), and finally into 1,005 specific industries (4-digit codes).

How SIC Codes Are Structured

Each digit in a SIC code adds specificity. Take the example of a company that prints books:

• Division D (codes 20-39) — Manufacturing
• Major Group 27 — Printing, Publishing, and Allied Industries
• Industry Group 273 — Books
• Industry 2732 — Book Printing

This hierarchical structure lets you zoom in or out. If you want all manufacturing companies, you filter for SIC codes 20-39. If you want only book printers specifically, you filter for SIC code 2732.

The SIC system was last updated in 1987 by the Office of Management and Budget. It has not been revised since, which is both its greatest limitation and one reason it persists — the codes are stable and predictable, making them useful for long-term data comparison.

2. What Is a NAICS Code?

A NAICS code (North American Industry Classification System code) is a six-digit number that classifies a business by its primary economic activity. NAICS was developed jointly by the statistical agencies of the United States, Canada, and Mexico and officially adopted in 1997 as the replacement for the SIC system.

NAICS organizes all economic activity into 20 industry sectors, which break down into subsectors, industry groups, NAICS industries, and national industries — totaling 1,170 specific industry categories. That is 165 more categories than SIC, with 358 industries recognized in NAICS that had no equivalent under SIC — the majority of which are in the services sector.

How NAICS Codes Are Structured

Each of the six digits in a NAICS code represents a level of specificity:

• Digits 1-2 — Sector (the broadest level, 20 sectors total)
• Digit 3 — Subsector
• Digit 4 — Industry Group
• Digit 5 — NAICS Industry
• Digit 6 — National Industry (country-specific detail for US, Canada, or Mexico)

For example, consider a residential building contractor:

• 23 — Construction (sector)
• 236 — Construction of Buildings (subsector)
• 2361 — Residential Building Construction (industry group)
• 23611 — Residential Building Construction (NAICS industry)
• 236115 — New Single-Family Housing Construction (national industry)

The first five digits are generally consistent across the US, Canada, and Mexico, which allows for direct comparison of economic data across the three countries. The sixth digit is country-specific.

Unlike SIC, NAICS is revised approximately every five years to keep pace with changes in the economy. Major revisions occurred in 2002, 2007, 2012, 2017, and 2022. The next revision is expected in 2027. This means NAICS can accommodate emerging industries — like streaming media services, drone manufacturing, or AI consulting — that did not exist when the system was created.

3. SIC vs NAICS — Key Differences

Although both systems classify businesses by their primary activity, SIC and NAICS differ significantly in structure, scope, and philosophy. Here is a side-by-side comparison:

The most fundamental difference is philosophical. SIC grouped industries using a mix of production-oriented and market-oriented logic — meaning some codes were based on what a company makes and others on who a company sells to. This inconsistency crept in over decades of ad hoc revisions. NAICS, by contrast, uses a single, consistent production-oriented concept: businesses that use similar processes to produce goods or services are grouped together, regardless of who their customers are.

4. The 20 NAICS Sectors (Complete Reference)

NAICS organizes all economic activity into 20 top-level sectors. Each sector is identified by a two-digit code. Here is the complete list with descriptions:

Each of these 20 sectors breaks down into hundreds of more specific subcategories. For instance, Sector 23 (Construction) includes everything from new single-family home builders (NAICS 236115) to highway and street construction (NAICS 237310) to electrical contractors (NAICS 238210). The six-digit NAICS code gives you the precision to target exactly the type of business you are looking for.

5. The 10 SIC Divisions (Complete Reference)

The SIC system uses 10 broad divisions, each covering a range of two-digit major groups:

• Division A (01-09) — Agriculture, Forestry, and Fishing
• Division B (10-14) — Mining
• Division C (15-17) — Construction
• Division D (20-39) — Manufacturing
• Division E (40-49) — Transportation, Communications, Electric, Gas, and Sanitary Services
• Division F (50-51) — Wholesale Trade
• Division G (52-59) — Retail Trade
• Division H (60-67) — Finance, Insurance, and Real Estate
• Division I (70-89) — Services
• Division J (91-99) — Public Administration

Notice how SIC groups all services into a single division (Division I, codes 70-89), while NAICS spreads service industries across multiple dedicated sectors — healthcare, professional services, education, food services, and so on. This is one of the main reasons NAICS was created: the services sector grew from roughly half of the US economy in the 1930s to over 80% by the 1990s, and a single "Services" bucket could not capture that diversity.

6. How to Find a SIC or NAICS Code

Whether you need to look up your own company's code or find the code for a target industry, here are the best free resources:

For NAICS Codes

• US Census Bureau (census.gov/naics) — The official source. Search by keyword or browse the full hierarchy. Includes definitions, cross-references, and examples of what each code includes and excludes.
• NAICS Association (naics.com) — Keyword search tool with plain-language descriptions. Also offers SIC-to-NAICS crosswalk tables.
• SBA Size Standards (sba.gov) — If you need your NAICS code for an SBA loan application or government contracting, the SBA lists size standards by NAICS code.

For SIC Codes

• OSHA SIC Manual (osha.gov) — The official SIC code reference, hosted by the Department of Labor.
• SEC EDGAR (sec.gov/cgi-bin/browse-edgar) — Public company filings still use SIC codes. You can look up any public company's SIC classification here.
• SICCODE.com — Searchable SIC and NAICS database with crosswalk tools for converting between the two systems.

How Codes Are Assigned

A business does not formally "apply" for a SIC or NAICS code. Instead, statistical agencies assign codes based on information a business provides on forms like the Employer Identification Number (EIN) application, census surveys, and tax filings. The code is determined by the establishment's primary activity — the activity that generates the most revenue.

This is an important distinction: a hardware store that also offers locksmith services would be classified under Retail Trade (for hardware), not under Other Services (for locksmithing), because hardware sales are the primary revenue source. A single business gets one primary code, even if it has multiple lines of business.

Every US business is assigned a SIC and/or NAICS code based on its primary economic activity.

7. Practical Uses for SIC and NAICS Codes

Industry classification codes are not just a government bureaucracy exercise. They have direct, practical applications across business, marketing, finance, and compliance.

Sales and Marketing Targeting

This is the most common commercial use. If you sell commercial insurance, you can use SIC or NAICS codes to filter a business database and find every construction company, manufacturing firm, or trucking business in your territory. If you sell payroll software, you might target retail businesses and restaurants with 10-50 employees. The codes let you transform a broad business database into a precision-targeted lead list.

As covered in our B2B lead generation guide, combining industry code filters with geographic targeting is one of the most effective segmentation strategies available. Filtering for healthcare companies in Florida or professional services firms in New York creates highly targeted lists for outreach.

Market Research and Competitive Analysis

NAICS codes power most of the economic statistics published by federal agencies. The US Census Bureau's Economic Census, County Business Patterns, and Annual Business Survey all use NAICS codes. If you want to know how many real estate companies operate in a specific state, what the average revenue is for wholesale distributors, or how employment in information technology has changed over the past decade, you need the NAICS code to pull the data.

Government Contracting

The Small Business Administration (SBA) uses NAICS codes to determine whether a business qualifies as "small" for government contracting purposes. Each NAICS code has its own size standard — either a maximum number of employees or a maximum annual revenue threshold. A company classified under NAICS 236115 (New Single-Family Housing Construction) has a different size standard than one classified under NAICS 541511 (Custom Computer Programming Services). If your NAICS code is wrong, you might be disqualified from contracts you should be eligible for.

Insurance and Risk Classification

Insurance underwriters use both SIC and NAICS codes to assess risk. A business classified as a roofing contractor (SIC 1761) carries a fundamentally different risk profile than an accounting firm (SIC 8721). Workers' compensation, general liability, and professional liability premiums are all influenced by the industry classification. An incorrect code can mean overpaying for coverage or, worse, having a claim denied because the policy was issued under the wrong classification.

Banking and Financial Compliance

Banks use NAICS and SIC codes for BSA (Bank Secrecy Act) and Patriot Act compliance. Certain industry codes are flagged as higher risk for money laundering, requiring enhanced due diligence during the account opening process. The codes help banks systematically identify which customers need additional scrutiny based on their industry classification.

Tax Incentives

Some state and local governments offer tax incentives to businesses in specific NAICS sectors — for example, manufacturing tax credits, technology zone exemptions, or agricultural subsidies. Your NAICS code determines whether your business qualifies for these programs.

8. Converting Between SIC and NAICS

One of the most common questions people have is whether you can directly convert a SIC code to a NAICS code. The short answer: not directly.

Because the two systems use different classification logic — SIC uses a mix of production and market-based grouping, while NAICS uses consistent production-based grouping — there is no clean one-to-one mapping. A single SIC code can map to multiple NAICS codes, and vice versa.

For example, a company classified under SIC 7359 (Equipment Rental and Leasing, Not Elsewhere Classified) could map to several different NAICS codes depending on what specific equipment it rents — construction equipment rental falls under NAICS 532412, while office machinery rental falls under NAICS 532420.

Using Crosswalk Tables

The US Census Bureau publishes official "crosswalk" tables that show the relationships between SIC and NAICS codes. These are available for free at census.gov and provide the best available mapping between the two systems. However, they should be used as approximate guides — always verify against the actual code definitions to confirm the match makes sense for the specific business in question.

The NAICS Association (naics.com) and SICCODE.com also provide interactive crosswalk tools that let you enter a SIC code and see the corresponding NAICS codes, or vice versa.

9. Which System Should You Use?

The answer depends on what you are doing:

Use NAICS when:

• Filing federal statistical reports or Census surveys
• Applying for SBA loans or government contracts
• Researching current economic data (most federal datasets use NAICS)
• Classifying modern, service-oriented, or technology businesses
• Comparing US economic data with Canada or Mexico

Use SIC when:

• Filing SEC reports (the SEC still requires SIC codes)
• Working with insurance underwriting and risk classification
• Using marketing databases that include SIC codes for targeting
• Analyzing historical economic data (pre-1997 datasets use SIC)
• Working with legacy systems that have not converted to NAICS

Use both when:

• Building a comprehensive business database — many datasets include both codes
• Conducting broad market research that spans historical and current data
• Your work touches multiple systems or agencies with different requirements

In practice, many business databases — including the USCompaniesList database — include both SIC and NAICS codes on each record. This gives you the flexibility to filter and segment using whichever system is most appropriate for your specific use case.