HS Code Structure Explained: How to Read the 6-Digit System

Your supplier sends you an HS code. Your broker files a different one. Both tell you they are correct. If you do not understand how the code is structured, you have no way to know who is right.

This guide explains how HS codes are built, what each digit group means, and how to read any code so you can catch classification errors before customs does.

What is the structure of an HS code?

An HS code is not a random string of numbers. It follows a hierarchical tree structure with four levels, each narrowing the classification from a broad industry category down to a specific product type. According to the World Customs Organization (WCO), the internationally standardized portion is always the first six digits.

Using HS code 8471.30 as an example:

• 84 — Chapter 84: Machinery and mechanical appliances, computers

• 8471 — Heading 8471: Automatic data processing machines (computers)

• 8471.30 — Subheading: Portable digital computers (laptops, tablets)

Read left to right, each pair of digits zooms in. Chapter identifies the industry. Heading identifies the product group. Subheading identifies the specific item. That six-digit subheading is the same in every WCO member country—over 200 countries and economies worldwide.

How is the full HS system organized?

The complete Harmonized System (HS 2022, the current edition) is structured into four levels according to the WCO:

• 21 Sections — Broad economic categories (e.g., Section XVI: Machinery and mechanical appliances)

• 96 Chapters — Identified by two-digit numbers (e.g., Chapter 84: Machinery)

• 1,200+ Headings — Four-digit codes identifying product groups

• 5,600+ Subheadings — Six-digit codes, the universal classification level

The chapters generally progress from raw materials to complex manufactured goods. Chapter 1 covers live animals. Chapter 84 covers machinery. Chapter 97 covers works of art. That progression is intentional—it makes the system navigable once you understand the logic.

What happens after the sixth digit?

After the sixth digit, each country adds its own national extensions. The first six digits are universally standardized. Everything after that is country-specific and determines your actual duty rate.

• United States: 10 digits total — HTS code (imports, administered by USITC) or Schedule B (exports, administered by US Census Bureau)

• Korea: 10 digits total — HSK code

• European Union: 8 digits (Combined Nomenclature) with additional statistical codes up to 10 digits

This is why your Korean supplier's full 10-digit code does not apply to your US or EU import filing. The first six digits are shared. The last four are not. Your customs broker must reclassify under your country's tariff schedule—the supplier's code is a starting point, not the answer.

According to the International Trade Administration (ITA), while the 6-digit HS subheading will be identical across countries for the same product, the national extensions can differ significantly both across trading partners and between a single country's import and export classifications.

How do you read an HS code you have never seen before?

Start from the left and work right. Each two-digit group narrows the classification. You do not need to memorize codes—you need to know which direction to read and what each level represents.

Take HS code 0902.10:

• 09 — Chapter 9: Coffee, tea, maté and spices

• 0902 — Heading 0902: Tea, whether or not flavoured

• 0902.10 — Subheading: Green tea in packings not exceeding 3 kg

If someone classified a green tea shipment under Chapter 84 (machinery), you would catch it immediately—because Chapter 84 has nothing to do with food or beverages. The structure makes errors visible.

According to the WCO, classification decisions follow the General Rules for the Interpretation of the Harmonized System (GRI), applied in strict order. GRI 1 states that classification is determined first by the terms of the headings and any relevant legal notes. In practice, this means the product's function, composition, and form all matter—not just what the invoice calls it.

Why does the WCO update HS codes, and when?

The WCO updates the Harmonized System approximately every five years to reflect changes in technology and global trade patterns. The current edition, HS 2022, came into effect on January 1, 2022. Previous editions include HS 2017, HS 2012, and HS 2007.

Updates add new headings for emerging product categories, remove headings with low trade volume, and clarify classification rules. When a new edition takes effect, national tariff schedules must be updated to align—and any binding rulings you hold may need to be reviewed for continued validity.

For importers and exporters with recurring shipments, tracking HS revision cycles is part of compliance management. A code that was correct under HS 2017 may have a different subheading under HS 2022.

HS code structure: quick reference

• Digits 1–2: Chapter — identifies the broad industry or material category

• Digits 3–4: Heading — identifies the specific product group within the chapter

• Digits 5–6: Subheading — internationally standardized, same in all WCO member countries

• Digits 7–10: National extensions — country-specific, determines actual duty rate

• Current edition: HS 2022 (effective January 1, 2022)

• Your supplier's full code is a starting point — verify the national extension with your broker

• If a code doesn't match the product at the Chapter level, flag it immediately