A CPC number is a Cooperative Patent Classification code, an alphanumeric symbol assigned to a patent document to identify the specific technical subject matter of the invention. The system is maintained jointly by the United States Patent and Trademark Office and the European Patent Office, and its hierarchy holds roughly 250,000 classification entries covering every field of technology.1Cooperative Patent Classification. Guide to the CPC Every published patent carries at least one CPC number on its front page, and examiners, searchers, and applicants use those codes to locate technology by what it does rather than by the words used to describe it.
How to Read a CPC Number
Every CPC symbol follows the same left-to-right pattern, moving from broad category down to narrow technical detail. Take A01B 1/00. The first letter (A) identifies the section, the broadest category. The two digits that follow (01) identify the class within that section. The next letter (B) marks the subclass. After a space, a one- to three-digit number identifies the main group, and a forward slash separates it from a two- to six-digit subgroup number that captures the most specific detail.1Cooperative Patent Classification. Guide to the CPC
In that example, “A” is Human Necessities, “01” narrows to Agriculture, “B” specifies soil working in agriculture, and “1/00” identifies hand tools. The CPC builds on the International Patent Classification used worldwide but adds far more subdivisions. Where the IPC groups several related technologies under one code, the CPC often splits them into separate entries.
The Nine Sections
The CPC organizes all technology into eight main sections labeled A through H, plus a supplementary section Y. Each covers a broad domain:
- Section A: human necessities (agriculture, food, health, amusement)
- Section B: performing operations and transporting
- Section C: chemistry and metallurgy
- Section D: textiles and paper
- Section E: fixed constructions (buildings, mining, earth drilling)
- Section F: mechanical engineering, lighting, heating, weapons, blasting
- Section G: physics (instruments, computing, signaling)
- Section H: electricity (generation, conversion, distribution, electronic circuits, communication)
Sections A through H mirror the IPC’s structure. Section Y is unique to the CPC and does not replace the classification assigned from A through H. Instead, Y codes tag patents that touch emerging or cross-sectional technologies. Y02, for example, covers technologies for climate change mitigation under the frameworks of the Kyoto Protocol and Paris Agreement, so a solar panel patent might carry both an H classification and a Y02 tag.2United States Patent and Trademark Office. CPC Scheme – Y General Tagging of New Technological Developments Y10 serves a different purpose, accommodating technical subjects formerly covered by the old U.S. Patent Classification system’s cross-reference art collections and digests. Y10T is a temporary subclass that will eventually be phased out as legacy USPC content is absorbed into the main sections.
Scheme and Definitions Are Two Different Documents
Two official documents govern every CPC code, and confusing them is a common mistake. The CPC Scheme is the hierarchical tree of classification symbols organized from section down to subgroup. The CPC Definitions sit alongside the scheme and provide detailed textual explanations of what each code actually covers, including definition statements, relationships with other classification places, limiting references, glossaries, and special rules of classification.1Cooperative Patent Classification. Guide to the CPC
Two codes can look similar in the scheme’s shorthand titles but cover meaningfully different technology once you read their definitions. Anyone selecting a CPC code for a patent application should check the definitions, not just the scheme titles.
How to Look Up a CPC Number
The USPTO offers a free online classification search with two approaches. A Classification Text Search lets you enter keywords to search across CPC scheme titles and definitions. A Classification Symbol Lookup lets you enter a known CPC symbol to view its scheme entry, definition, or concordance to the IPC.3United States Patent and Trademark Office. Search Patent Classification Systems
The European Patent Office’s Espacenet database offers a classification search accepting CPC symbols with wildcard characters. Typing “A61K*” returns all documents classified in A61K and its subgroups. You can also browse the classification tree, select relevant codes, and copy them directly into a patent search form.4Espacenet. Espacenet – Classification Search
A practical workflow: start with a keyword search to find a handful of patents similar to the invention you’re researching, note the CPC codes assigned to those patents, then search for additional patents in the same classification. That second pass catches inventions that used completely different terminology in their titles and abstracts but cover the same technology.
Why Classification Codes Outperform Keywords
Keyword searching in patent databases has real limitations. Patent attorneys routinely draft applications using deliberately vague or unconventional language to make claims appear more novel. Synonyms, spelling variations between American and British English, and poor translations of foreign-language patents all mean a keyword search can miss critical prior art. CPC codes group inventions by what they actually do, regardless of how the inventor chose to describe them. Patent examiners rely heavily on classification codes during their own prior art searches.
How CPC Numbers Affect a Patent Application
When you file a patent application, it gets routed to a patent examiner whose expertise matches the assigned CPC classification. If the classification is wrong, the application may be reassigned through a classification challenge, where the initial examiner flags the mismatch and the application moves to an examiner in the correct technical area. That adds time to an already lengthy review.
Classification also shapes the quality of your prior art search. Under federal patent law, an invention cannot be patented if it was already patented, described in a publication, or in public use before the application’s effective filing date.5Office of the Law Revision Counsel. 35 U.S. Code 102 – Conditions for Patentability; Novelty Searching the wrong CPC subgroups can mean missing an existing patent that covers the same technology, which leads to a rejection that might have been avoided, or an issued patent vulnerable to later challenge.
Where CPC Numbers Appear on a Patent
Once a patent is published, its assigned CPC codes appear on the front page of the patent document and in all major patent databases, including the USPTO’s Patent Public Search, Google Patents, and Espacenet. Published applications carry CPC codes as well, not just granted patents. Examiners sometimes assign multiple CPC codes to a single patent when the invention spans more than one technical area, and invention-information codes are distinguished from additional-information codes to indicate which classifications relate to the core invention versus supplementary technical context.
A Note on Older Patents and USPC Codes
Before January 1, 2013, the USPTO used its own national system called the United States Patent Classification. On that date, the office switched to the CPC for classifying utility patents.6United States Patent and Trademark Office. Patent Classification The USPTO continues to maintain USPC classification only for plant and design patents, so if you’re working with those or with pre-2013 utility patents, you’ll still encounter USPC codes. The USPTO’s classification search page includes a statistical mapping tool that translates USPC codes into their most likely CPC equivalents by identifying which CPC classes most frequently co-occur with a given USPC code. The mapping is useful but imperfect; verify any suggested CPC code against the scheme and definitions rather than accepting the first result.3United States Patent and Trademark Office. Search Patent Classification Systems