How HSN codes are built
HSN (Harmonized System of Nomenclature) codes classify goods. The first two digits are the chapter, four digits the heading, six digits the sub-heading, and India uses eight digits for the full tariff item. For example, chapter 85 is electrical machinery, heading 8517 covers telephone sets including mobile phones.
Services use SAC (Services Accounting Codes), which all start with 99. Heading 9963 covers accommodation and food services, 9983 other professional services, and so on.