SIC vs NAICS Codes: Differences, History and How to Convert

Two industry classification systems, one confusing overlap. Here is why both still exist, how their structures differ, and how to convert a SIC code to NAICS correctly.

If you have ever filled out a business loan application, registered with a government portal, or looked up a company on the SEC's EDGAR system, you have probably run into two different "industry codes" for the same business: a 4-digit SIC code and a 6-digit NAICS code. They are not interchangeable, they do not map neatly onto each other, and different institutions ask for different ones. This guide explains where each system came from, how they differ structurally, who still asks for SIC, and how to convert between them without guessing.

A short history: from SIC (1930s) to NAICS (1997)

The Standard Industrial Classification (SIC) was developed by the U.S. federal government in the 1930s so that statistical agencies could describe the economy in a consistent way. It was revised several times over the decades, but the last full revision was published in 1987 — which means the SIC system still in circulation today reflects the economy of the late 1980s. There is no SIC code that cleanly describes an e-commerce marketplace, a streaming service, or an app developer, because those industries barely existed when the list was frozen.

That obsolescence, plus the North American Free Trade Agreement, drove the creation of the North American Industry Classification System (NAICS). It was developed jointly by the statistical agencies of the United States, Canada and Mexico under the guidance of the U.S. Office of Management and Budget (OMB), and it replaced SIC in U.S. federal statistics starting in 1997. Unlike SIC, NAICS is a living standard: it is reviewed on a five-year cycle, with revisions published in 1997, 2002, 2007, 2012, 2017 and 2022, the current version. The revision cycle is aligned with the U.S. Economic Census, which is conducted in years ending in 2 and 7.

The five-year cycle matters in practice because codes really do move. A well-known example: software publishers were SIC 7372 ("Prepackaged Software"), became NAICS 511210 ("Software Publishers") in 1997, and then moved to 513210 in the NAICS 2022 revision when the Information sector was restructured. If a form asks for your NAICS code, it is worth knowing which vintage the form expects.

Structural differences: 4 digits vs 6, product vs production process

The two systems differ in more than length. Here is a side-by-side view:

	SIC (1987)	NAICS (2022)
Code length	4 digits	6 digits
Hierarchy	Division (letter A–K) → 2-digit major group → 3-digit industry group → 4-digit industry	2-digit sector → 3-digit subsector → 4-digit industry group → 5-digit NAICS industry → 6-digit national industry
Classification concept	Mixed — industries grouped partly by product or market served	Production-oriented — establishments grouped by similar production processes
Geographic scope	United States only	United States, Canada and Mexico (comparable through the 5-digit level; the 6th digit is country-specific)
Maintenance	Frozen since 1987	Revised every 5 years; current version 2022

The conceptual difference is the most important one. SIC grouped industries in a somewhat ad hoc way — sometimes by what they make, sometimes by whom they sell to. NAICS applies a single consistent principle: establishments that use similar production processes belong in the same industry, regardless of who buys the output. That is why NAICS carved out an entire Information sector (sector 51) covering publishing, broadcasting, telecommunications and data services — activities that were scattered across manufacturing and services divisions under SIC. NAICS also introduced sectors that SIC never distinguished cleanly, such as Professional, Scientific, and Technical Services (54) and Health Care and Social Assistance (62).

Another practical consequence: because NAICS is more granular (six digits instead of four) and built on a different logic, there is no one-to-one mapping between the two systems. One SIC code commonly splits into several NAICS codes, and one NAICS code can absorb pieces of several SIC codes. SIC 5812 ("Eating Places"), for instance, corresponds to multiple NAICS industries under 7225 — full-service restaurants, limited-service restaurants, cafeterias, snack bars — depending on how the establishment actually operates.

Who still asks for a SIC code?

If NAICS replaced SIC in 1997, why do forms still ask for SIC codes almost thirty years later? Because several important institutions never fully migrated:

• The SEC. The Securities and Exchange Commission still assigns SIC codes to registrants on its EDGAR filing system, using its own maintained list of SIC codes. If you look up any public company's filings, you will see a 4-digit SIC code in the header. Analysts and screening tools built on EDGAR data therefore still speak SIC.
• Banks and lenders. Many underwriting systems, KYC workflows and legacy risk models were built around SIC and keep a SIC field, sometimes alongside NAICS. Loan applications frequently ask for one, the other, or both.
• Insurance companies. Commercial insurers have long used SIC-based classifications for underwriting and rating, and many still request a SIC code when quoting business policies.
• Commercial data providers. Business databases such as Dun & Bradstreet historically classified companies with SIC-based schemes, so purchased marketing lists and firmographic data often carry SIC codes.

Meanwhile, federal statistical agencies, the IRS (business activity codes on tax returns are NAICS-based), the SBA (size standards are defined by NAICS code), and government contracting systems all work in NAICS. In practice, an established U.S. business ends up needing both codes at different moments — which is exactly when conversion questions arise. A side note for non-U.S. readers: the United Kingdom's "SIC codes" used by Companies House belong to a different system (UK SIC 2007, derived from the EU's NACE classification) and are not the U.S. 1987 SIC discussed here.

How to convert SIC to NAICS

The authoritative source for conversion is the U.S. Census Bureau's concordance tables, published on the Census NAICS pages. The Census Bureau released official correspondence tables between the 1987 SIC and NAICS when the new system was introduced, and it publishes concordances between successive NAICS vintages (2017→2022 and so on) with every revision. Because the mapping is many-to-many, the tables do not give you "the" answer — they give you every valid correspondence, and you choose the one matching your primary business activity.

A sensible workflow looks like this:

1. Start from your SIC code and find all candidate NAICS codes it maps to. Our SIC to NAICS converter does this instantly: enter a 4-digit SIC code and it returns the corresponding NAICS codes with their official titles, flagging when a code splits into multiple targets.
2. Read the NAICS industry descriptions for each candidate and pick the one that describes what your establishment primarily does — the activity that accounts for most of your revenue or production. The NAICS lookup tool lets you search codes by keyword and browse the 2022 hierarchy, which helps when the candidates look similar on paper.
3. Check the vintage. If the form or database you are filling in was built years ago, it may expect a 2017 (or older) NAICS code. Where a code changed in 2022 — like the software publishers move from 511210 to 513210 — make sure you submit the vintage the recipient expects.
4. Converting the other way (NAICS to SIC, e.g. for an insurance application) works the same but in reverse: find which SIC industries feed into your NAICS code, then choose the SIC description closest to your actual activity.

Two cautions. First, resist the temptation to pick a "nicer" code: agencies, lenders and insurers use these codes for eligibility, pricing and risk decisions, and a mismatch between your stated code and your actual activity can cause real problems later. Second, self-classification is the norm — there is no central authority that certifies a company's NAICS code — so document why you chose the code you did. If you need to classify many company records at once, the CodeClassify API exposes the same SIC/NAICS lookups programmatically.

FAQ

Is the SIC system still used today?

Yes, in specific niches. The U.S. federal statistical agencies replaced SIC with NAICS starting in 1997, but the SEC still assigns SIC codes to companies that file on EDGAR, and many banks, insurers and commercial data providers keep SIC fields in their systems. That is why businesses often need both codes.

Do SIC and NAICS codes map one-to-one?

No. The relationship is many-to-many. A single 4-digit SIC industry can split into several 6-digit NAICS industries, and one NAICS industry can draw activities from several SIC industries. The U.S. Census Bureau publishes official concordance tables that list every valid correspondence, and you usually pick the NAICS code that matches your primary activity.

How often is NAICS updated, and which version is current?

NAICS is reviewed on a five-year cycle, with revisions published in 1997, 2002, 2007, 2012, 2017 and 2022. NAICS 2022 is the current version. Because codes can move between revisions, always check which vintage a form or agency expects before you submit a code.

This guide is for general information only. SIC/NAICS correspondences shown by our tools are suggestions based on the U.S. Census Bureau concordance tables, not official determinations. Industry classification is self-assigned; for filings with legal or financial consequences, verify the required code and vintage with the requesting agency (e.g. Census Bureau, OMB, SEC, SBA) or a qualified professional.