What is the difference between first unit of quantity and second unit of quantity?

The first unit of quantity refers to the first (if any) statistical reporting unit specified in the HTSUS (for imports) or Schedule B (for exports) applicable to the specific product classification selected. Note that not all product classification codes (10-digit HTS statistical reporting numbers for imports, or 10-digit schedule B numbers for exports) require importers or exporters to report a quantity measure.

The second unit of quantity refers to the second (if any) statistical reporting unit specified in the HTSUS or Schedule B applicable to the specific product classification selected. Note that most product classification codes do not require importers or exporters to report a second quantity measure.

Information as to whether importers must report a “first unit of quantity” and/or a “second unit of quantity” for any given product being imported is maintained in the HTSUS. In the example below all 10-digit statistical reporting numbers listed have a first unit of quantity of “No”, which represents number or units, and certain 10-digit statistical reporting numbers listed below (for example 8541.42.0010 is the first) also have a second unit of quantity of “W”, which represents watts. When the HTSUS show one or two “unit of quantity” next to a statistical reporting number, importers are required to submit data on those aggregated quantities (in addition to value) for its imports within their entry summary paperwork.