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Intellectual Property Rights - Law and Practice · Patent Databases and Patent Information System

Patent Classification Systems: IPC and CPC Explained

Updated 11 October 2026 · Fact-checked

A patent classification system sorts patent documents into technical categories using coded symbols. The International Patent Classification (IPC) is the global WIPO-administered scheme. The Cooperative Patent Classification (CPC) is a finer scheme built on the IPC, jointly run by the EPO and USPTO. You use the symbols to search and retrieve patents by technology.

Understand Patent Classification Systems

A patent office holds millions of documents. Keywords alone fail because inventors describe the same idea in different words, in different languages. A patent classification system fixes this. Every patent document is given one or more codes that describe its technology, whatever words it uses.

The International Patent Classification (IPC) is a hierarchical scheme created under the Strasbourg Agreement and administered by WIPO. It divides all technology into eight sections, labelled A to H. A is Human Necessities, B is Performing Operations and Transporting, C is Chemistry and Metallurgy, D is Textiles and Paper, E is Fixed Constructions, F is Mechanical Engineering, Lighting, Heating, Weapons and Blasting, G is Physics, and H is Electricity. Each section is divided into classes, then subclasses, then main groups and subgroups. The deeper you go, the narrower the technology.

An IPC symbol is read from left to right. Take A61K 9/00. A is the section, 61 is the class, K is the subclass, 9 is the main group, and /00 shows it is a main group (a subgroup has a number other than 00 after the slash). The scheme is revised regularly and a new edition comes into force from time to time, so the classification given to a document can be re-checked against the current edition.

The Cooperative Patent Classification (CPC) is a joint scheme of the European Patent Office and the US Patent and Trademark Office. It is based on the IPC structure, using the same sections and symbol format, but it has many more subdivisions. It adds a Section Y for cross-sectional technologies. CPC is therefore better for a detailed prior-art search, while IPC is the common language used by almost every patent office, including the Indian Patent Office.

Why this matters for you: classification is a search tool. It is used by examiners to find prior art, by applicants to check novelty before filing, and by businesses to map technology trends and freedom to operate. Classification does not decide whether an invention is patentable. That is decided under the Patents Act, 1970. Note also that the term of a patent runs under section 53 from the filing date (20 years), and not from any classification step.

Key rules to remember

IPC symbol structure
Section (letter) + Class (2 digits) + Subclass (letter) + Main group / Subgroup (numbers)
Example: A61K 9/00. A = section, 61 = class, K = subclass, 9/00 = main group. A subgroup follows the slash with digits other than 00.
IPC sections
A Human Necessities | B Operations and Transporting | C Chemistry and Metallurgy | D Textiles and Paper | E Fixed Constructions | F Mechanical Engineering, Lighting, Heating, Weapons | G Physics | H Electricity
Eight sections in all. Learn them in order A to H.
IPC hierarchy
Section → Class → Subclass → Main group → Subgroup
Moves from broad to narrow technology.
CPC relationship to IPC
CPC = IPC-based structure + finer subdivisions + Section Y
CPC is a joint EPO and USPTO scheme. It is more detailed than IPC but follows the same format.
Term of a patent (for context)
20 years from the date of filing (section 53(1)); for PCT applications designating India, from the international filing date
Classification does not change the term.

How to solve Patent Classification Systems questions

Use this method for any question on patent classification, whether it asks you to explain, compare or decode a symbol.

  1. 1Define a patent classification system in one line: it organises patent documents by technology using coded symbols, to help search and retrieval.
  2. 2Name the scheme asked about: IPC (WIPO, Strasbourg Agreement) or CPC (EPO and USPTO, built on IPC).
  3. 3Explain the structure: eight sections A to H, then class, subclass, main group and subgroup, from broad to narrow.
  4. 4If a symbol is given, decode it left to right and state what each part means.
  5. 5If a comparison is asked, use set headings: administrator, scope, level of detail, who uses it, and use in search.
  6. 6State the practical use: prior-art search by examiners, novelty checks by applicants, technology mapping and freedom-to-operate checks by businesses.
  7. 7Add a limit: classification is only a search aid. Patentability and rights come from the Patents Act, 1970.
  8. 8Close with a one-line conclusion that answers the exact question.

Quickest way: Decode and compare in 60 seconds

When to use it: Use when a short-note or 5-mark question asks you to explain IPC or distinguish IPC from CPC.

  1. Write the one-line definition.
  2. Write the eight sections A to H in a single line.
  3. Show one decoded symbol such as A61K 9/00.
  4. Write two or three comparison points: IPC is by WIPO and global, CPC is by EPO and USPTO and more detailed.
  5. End with the search use.

Common mistakes in Patent Classification Systems

  • Saying CPC is administered by WIPO.

    Both schemes look alike and students link every international scheme to WIPO.

    Fix: Remember: IPC is WIPO's. CPC is the joint scheme of the EPO and USPTO.

  • Listing the wrong number of IPC sections or mixing up letters.

    Students memorise only a few sections and guess the rest.

    Fix: Learn all eight, A to H, with a memory line for each. Check against the list in this page.

  • Reading an IPC symbol in the wrong order, for example treating K as the class.

    Students do not know the left-to-right pattern of letter, digits, letter, numbers.

    Fix: Read section letter, class digits, subclass letter, then the group numbers after the space and slash.

  • Claiming classification decides whether an invention is patentable.

    Students confuse a search tool with a legal test.

    Fix: State that classification only organises documents. Patentability is tested under the Patents Act, 1970.

  • Saying CPC replaces IPC.

    CPC is more detailed, so students assume it is a replacement.

    Fix: Say CPC is built on the IPC structure and extends it. IPC remains the common international scheme.

Worked examples

Example 1

Explain the International Patent Classification and decode the symbol H04L 9/32. (Answer for about 8 marks.)

Show the solution
  1. Definition: the IPC is a hierarchical scheme administered by WIPO under the Strasbourg Agreement. It classifies patent documents by technology so that they can be searched and retrieved irrespective of language or wording.
  2. Structure: it has eight sections A to H. Each section is split into classes, subclasses, main groups and subgroups, from broad to narrow.
  3. Decoding H04L 9/32: H is the section, Electricity.
  4. 04 is the class, which covers electric communication technique.
  5. L is the subclass, covering transmission of digital information.
  6. 9/32 is the group: 9 is the main group number and 32 after the slash shows it is a subgroup, because it is not 00.
  7. Use: examiners use this symbol to find prior art on the same technology, and applicants use it to check novelty before filing.
  8. Limit: the symbol only helps in search. Whether the invention is patentable is decided under the Patents Act, 1970.

Answer: The IPC is WIPO's hierarchical technology code. H04L 9/32 reads: section H (Electricity), class 04, subclass L, main group 9, subgroup 32. It is a search aid, not a test of patentability.

Example 2

Distinguish between IPC and CPC. Ravi, a Pune-based engineer, wants to run a detailed prior-art search before filing. Which scheme should he rely on, and why?

Show the solution
  1. Administrator: IPC is administered by WIPO. CPC is a joint scheme of the EPO and USPTO.
  2. Basis: IPC is the common international scheme. CPC is built on the IPC structure and uses the same sections A to H.
  3. Detail: CPC has many more subdivisions than IPC. It also adds Section Y for cross-sectional technologies.
  4. Usage: nearly all patent offices, including India's, use IPC. CPC is used mainly by the EPO and USPTO and widely in searchable databases.
  5. Application to Ravi: he needs fine-grained results, so CPC symbols narrow down the technology better.
  6. Safeguard: he should also search by IPC, because it is the symbol present on documents from almost all offices, and combine with keywords.
  7. Conclusion: use CPC for depth, IPC for breadth, and neither replaces keyword and legal analysis.

Answer: IPC is WIPO's global scheme; CPC is the EPO and USPTO scheme built on IPC with finer subdivisions and Section Y. Ravi should lead with CPC for a detailed search and cross-check with IPC and keywords.

Exam tips

  • Always give the full forms and the administrator: IPC with WIPO, CPC with EPO and USPTO.
  • Write the eight sections A to H in one line. It is an easy scoring point.
  • When a symbol is given, decode it part by part in a short list. Do not just describe it in general.
  • Use headings in comparison answers and end with a practical conclusion for the facts given.
  • Add a one-line limit that classification is a search tool, not a test of patentability under the Patents Act, 1970.

Practice questions from Patent Databases and Patent Information System

Patent Classification Systems: frequently asked questions

What is the difference between IPC and CPC?

IPC is administered by WIPO and is used by almost all patent offices. CPC is a joint scheme of the EPO and USPTO, built on the IPC structure with many more subdivisions and an extra Section Y. CPC gives finer search results, while IPC is the common global language.

How do I find the IPC class of a patent?

Open the patent document in a patent database and look at the bibliographic data. The IPC symbols are printed there, usually as a field labelled IPC or International Classification. You can also search a database by IPC symbol to find other patents in the same technology.

How many sections does the IPC have?

The IPC has eight sections, labelled A to H. A is Human Necessities and H is Electricity. Each section is divided into classes, subclasses, main groups and subgroups.

Does the classification of a patent affect its term or validity?

No. Classification only organises documents for search. The term of a patent is 20 years from the filing date under section 53, and for PCT applications designating India it runs from the international filing date. Validity depends on the Patents Act, 1970, not on the class.