NAICS is a two-through-six-digit hierarchical classification code system, offering five levels of detail. Each digit in the code is part of a series of progressively narrower categories, and the more digits in the code signify greater classification detail. The first two digits designate the economic sector, the third digit designates the subsector, the fourth digit designates the industry group, the fifth digit designates the NAICS industry, and the sixth digit designates the national industry.
A complete and valid NAICS code contains six digits.
In developing NAICS, the United States, Canada, and Mexico agreed that the 5-digit codes would represent the level at which the system is comparable among the three countries. The sixth digit allows for each of the countries to have additional detail (i.e., subdivisions of a 5-digit category). In cases where the U.S. did not choose to create additional detail, the 5- and 6-digit categories within U.S. NAICS are the same, and the 6-digit US NAICS code ends in zero. In some hierarchical presentations, the 6-digit code is omitted where it is the same as the 5-digit category.