How Are NAICS Codes Structured? The 6-Digit Hierarchy Explained

A NAICS code is not a random number. It is an address in a tree that classifies the entire North American economy. Once you understand the tree, you can read any NAICS code like a map — knowing instantly what sector a business is in, how specific the classification is, and where to look for related codes.

We work with NAICS codes daily at trueNAICS, classifying companies from Veridion's database of over 120 million business records. Here is how the structure actually works, with the kind of detail that matters when you are choosing a code for insurance, contracting, or compliance.

The Tree: Six Levels Deep

NAICS organizes every economic activity into a hierarchy with six levels. Each level adds one digit, and each digit adds specificity:

The 2022 revision contains 2,129 total codes when you count every level. You can explore the full hierarchy interactively in the NAICS Directory.

Reading a Code: 541512 Step by Step

Let us decode 541512 — Computer Systems Design Services — one digit at a time.

54 — Professional, Scientific, and Technical Services

The first two digits identify the sector. Sector 54 covers businesses that sell expertise: lawyers, accountants, architects, engineers, scientists, consultants, and technology firms. If a business's primary value comes from knowledge rather than physical goods, it probably starts with 54.

541 — Professional, Scientific, and Technical Services

The third digit narrows to the subsector. Sector 54 happens to have only one subsector (also 541), but most sectors have several. Manufacturing (31-33), for example, splits into subsectors like Food (311), Beverages (312), Textiles (313), Wood (321), Chemicals (325), and a dozen more.

5415 — Computer Systems Design and Related Services

Now we are at the industry group level. Within all of professional services, this four-digit code isolates companies that design, integrate, and manage computer systems. It excludes law firms (5411), accounting firms (5412), engineering firms (5413), and every other professional service type — they each have their own industry group.

54151 — Computer Systems Design and Related Services

The five-digit level is the NAICS industry, and this is where international alignment happens. The US, Canada, and Mexico all agree that 54151 means computer systems design work. This is the level used for cross-border trade statistics and international comparisons.

541512 — Computer Systems Design Services

The sixth digit is where each country adds its own detail. The US splits 54151 into four national industries:

• 541511 — Custom Computer Programming Services
• 541512 — Computer Systems Design Services
• 541513 — Computer Facilities Management Services
• 541519 — Other Computer Related Services

A custom software development shop is 541511. A firm that designs and integrates IT infrastructure is 541512. A managed services provider is 541513. These distinctions matter for insurance (different liability profiles), SBA size standards, and industry benchmarking.

Canada and Mexico may split the same five-digit code differently at the sixth digit, which is why NAICS codes are only directly comparable across countries at the five-digit level.

All 20 Sectors at a Glance

Every NAICS code starts with one of these sector prefixes:

Three sectors span multiple two-digit ranges: Manufacturing (31-33), Retail Trade (44-45), and Transportation (48-49). This is because those sectors are so large that a single two-digit prefix cannot accommodate all their subsectors within the numbering system.

Browse any sector down to its six-digit codes in the NAICS Directory.

Why the Sixth Digit Is the One That Matters

For most practical purposes — insurance pricing, SBA eligibility, tax benchmarking — you need the full six-digit code. Here is what happens at each level of precision:

Two digits (54) tells an insurance underwriter that you are in professional services. That is like telling a doctor you feel "not great." It is not actionable.

Four digits (5415) narrows it to computer systems work. Better, but it still groups custom programmers, systems integrators, managed service providers, and miscellaneous IT firms together — each with different risk profiles and SBA thresholds.

Six digits (541512) pins down exactly what kind of computer work you do. Your underwriter can now pull industry-specific loss data. Your SBA size standard is precisely defined. The IRS knows which industry average to benchmark your returns against.

The practical difference is not small. Consider construction: the four-digit code 2381 covers "Foundation, Structure, and Building Exterior Contractors." Within that group, 238160 (Roofing Contractors) and 238170 (Siding Contractors) have different workers' compensation rates because their workplace injury profiles differ. Using the four-digit code would average them together, which is too imprecise for premium calculation.

How NAICS Connects to Other Systems

NAICS is not the only industry classification system in the world. Three others come up frequently:

SIC (Standard Industrial Classification) — The predecessor to NAICS, still used by the SEC and some insurance carriers. SIC uses four digits and has not been updated since 1987. Convert with our SIC to NAICS crosswalk.

NACE (Nomenclature of Economic Activities) — The European Union's standard, derived from the UN's ISIC system. If you are doing business in Europe or comparing transatlantic data, you may need NACE-to-NAICS mapping. Use our NACE to NAICS crosswalk.

ISIC (International Standard Industrial Classification) — The UN's global framework that most national systems (including NAICS and NACE) broadly derive from. Convert with our ISIC to NAICS crosswalk.

None of these mappings are one-to-one because each system carves up the economy differently. But the crosswalk tools on trueNAICS give you the closest available equivalents.

Practical Tips for Choosing the Right Code

Always use six digits. Any form that asks for your NAICS code means the six-digit national industry code. A two- or four-digit code is not specific enough for insurance, contracting, tax filing, or SBA registration.

Match your primary revenue source. If your business does three things but 70% of revenue comes from one activity, that activity determines your primary NAICS code. Secondary codes can capture the rest.

Read the official definition, not just the title. NAICS code titles can be misleading. Two codes might sound similar but have important distinctions in their Census Bureau definitions. Before committing to a code, check its full description in the NAICS Directory.

Cross-reference with data providers. What you think your NAICS code should be and what data providers actually assign can differ. Use Company Search to see how AI classification categorizes your business based on evidence from Veridion's database — it gives you an independent data point to compare against your self-assessment.

Update when your business changes. If you pivoted from consulting to SaaS, from residential to commercial construction, or from retail to wholesale — your NAICS code needs to follow. Outdated codes create mismatches in every system that references them.

Explore the Hierarchy

Once you understand the six-level structure, navigating NAICS becomes intuitive. Start broad, narrow down, and always end at six digits.

• Search by keyword — find codes matching your business activity
• Browse the NAICS Directory — navigate the full tree visually
• Look up a company — see AI-determined classification from real data
• Convert from SIC, NACE, or ISIC — map codes between systems