NAICS vs SIC Codes: What Is the Difference?

NAICS is the current standard for classifying US businesses by industry, and SIC is the older system it replaced. Both turn "what does this company do" into a number you can filter on.

Key takeaways

• NAICS has up to six digits and a clear hierarchy. SIC has four digits and is the older of the two.
• The codes do not map one to one. A NAICS code and a SIC code for the same company can describe different slices of an industry.
• For a new lead list, start with NAICS. Use SIC when a regulator, a list or a customer already hands you SIC codes.
• LeadOcean takes both as filters: naics and sic, on people search and company search.

What it is

An industry code is a short number that places a business in a category, so lists, statistics and filters can group companies the same way.

NAICS stands for North American Industry Classification System. The US Census Bureau describes it as the standard federal statistical agencies use to classify business establishments (source: Census Bureau, NAICS guidance, checked September 2026). It groups establishments by the similarity of the processes they use to produce goods or services.

SIC is the Standard Industrial Classification. Its detailed industries are four-digit codes. In 1997 the Office of Management and Budget adopted NAICS to replace the 1987 SIC for statistical purposes (OMB notice, 62 FR 17288, checked October 2026). SIC still turns up in legacy lists and databases.

How it works

NAICS reads left to right. Each extra digit narrows the category. Per the Census Bureau, the levels are:

1. Sector: 2 digits.
2. Subsector: 3 digits.
3. Industry group: 4 digits.
4. NAICS industry: 5 digits.
5. National industry: 6 digits.

Three sectors use a range of two-digit codes: Manufacturing (31-33), Retail Trade (44-45) and Transportation and Warehousing (48-49). The Census Bureau lists twenty sectors in total.

Worked example, taken from the Census page. A boat dealer sits in sector 44-45 (Retail Trade), subsector 441 (Motor Vehicle and Parts Dealers), industry group 4412 (Other Motor Vehicle Dealers) and NAICS industry 44122. The national industry is 441222, Boat Dealers.

Stop at 4412 and you get every kind of "other" vehicle dealer. Go to 441222 and you get boat dealers only. More digits means a tighter list and fewer matches.

SIC works the same way in spirit, with fewer levels to choose from. You pick a four-digit code and get everything filed under it.

Two practical rules follow from the NAICS levels. First, a code is a string, not a number, so keep it quoted and keep any leading zeros. Second, say how many digits you used when you share a list. "NAICS 44" and "NAICS 441222" are very different asks, and a teammate who reruns the filter needs to match yours.

NAICS vs SIC

NAICS is more detailed and more current. SIC is simpler and shows up in older data. Here is how they compare in practice.

Pick the code that matches how you describe the buyer. If you sell to boat dealers, a six-digit NAICS code names them exactly. If you sell to "retailers", a two-digit sector is enough. Precision costs coverage, so choose the loosest code that still keeps out the wrong companies.

The two systems were built at different times and cut industries differently. Treat any NAICS to SIC mapping as approximate. Check a few companies by hand before you trust a crosswalk for a whole list.

When it matters

Pick the system by where your input comes from. Three common cases.

You are building a new target list

Use NAICS. It has more levels, so you can start wide at 4 digits and narrow later. It is also the code your finance, ops or partner teams are more likely to quote today.

You inherited a list or a spec in SIC

Use SIC. Do not convert a list to NAICS just to filter it. Pass the SIC codes you were given and compare the result against your source list.

You are cleaning or segmenting an existing database

Check which system your records use before you filter. A column of four-digit codes is probably SIC. A column with five or six digits is NAICS. Mixed columns are common after a CRM merge, so split the rows by code length and filter each group with its own field.

You want a larger, safer list

Do not rely on codes alone. A code only matches companies that have one on file, so counts run small. Pair the code with an industry name or keywords and compare. On LeadOcean, industry is a closed list of 534 values and does not depend on a code being on file.

How LeadOcean handles it

LeadOcean has two filters, naics and sic. Both are arrays of strings on POST /v1/people/search and POST /v1/companies/search. They are free text, not a closed list, so there is no enum to look up.

Test the code before you build on it. In our runs on 2026-10-01, some naics and sic values returned a count and others returned unsupported_filters. The free count tool does not apply these filters reliably, so we do not quote code counts here.

A search costs 1 record per company returned. Sizing is free: send count=true in the URL (not the body) with limit set to 1.

curl -X POST "https://api.leadocean.io/v1/companies/search" \
  -H "x-api-key: $LEADOCEAN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "naics": ["5411"],
    "limit": 25
  }'

The same call with the older code system:

curl -X POST "https://api.leadocean.io/v1/companies/search" \
  -H "x-api-key: $LEADOCEAN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "sic": ["7372"],
    "limit": 25
  }'

You can also ask from an AI agent. Connect the MCP server at https://api.leadocean.io/mcp (see the VS Code setup) and ask for companies by code. For step-by-step filtering, see find companies by NAICS code and find companies by SIC code. More posts are in the blog.

The free plan has 1,000 records, one-off, no card. Pro is $499 a month. Details are on the pricing page.

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