An introduction to the Patent Classification System

Intellectual Property offices use classification systems to classify inventions into technology areas. Here we explain the systems used and how they help with searching.

Classification Systems

The International Patent Classification (IPC) is an internationally recognised classification system maintained by the World Intellectual Property Organization (WIPO) and used in more than 110 countries worldwide.

In the IPC, technology is divided into eight main sections: A Human necessities; B Performing operations, transporting; C Chemistry, metallurgy; D Textiles, paper; E Fixed constructions; F Mechanical engineering, lighting, heating, weapons, blasting; G Physics; and H Electricity.

Each classification code has five different levels: a section, class, subclass, group and subgroup.  For example, a fountain pen with a retractable nib might be classified as follows:

SectionBPerforming operations; transporting
ClassB43Writing or drawing implements; bureau accessories
SubclassB43KImplements for writing or drawing
GroupB43K5Pens with ink reservoirs in holders, e.g. fountain-pens
SubgroupB43K 5/16With retractable nibs

The Cooperative Patent Classification (CPC) is a patent classification system developed in partnership between the USPTO and the EPO and used by more than 45 patent offices worldwide.  The CPC is an extension of the IPC, and further classifies patent documents into specialised categories. In addition to section A-H, the CPC has a ninth section Y for tagging emerging technologies or technologies spanning several sections of the CPC.

The IPC classification code given to a patent document can be seen on its front page (INID code 51).  The European search report shows both the classification code given to the application and the classification codes of the technical fields searched (IPC and CPC).

Classification codes for a particular application are selected by the relevant IP office, rather than being chosen by the applicant. In some cases, it can be helpful, though, to consider in which class or classes an application will preferably be placed and to frame the specification accordingly.


Patent searching is used to identify prior art for new applications and to find patents and applications that may be relevant for third party freedom to operate. However, keyword searching alone can lead to an incomplete search, particularly when patent documents use different languages or terminologies. Classification codes are a useful tool for online searching.  Many patent databases, including the EPO’s espacenet database, allow searches using both IPC and CPC. The espacenet database has a dedicated classification search section and enables the IPC/CPC to be searched by keyword.

Classification codes allows broad searching within a section, class or subclass, or more focussed searching using the group or subgroup. It can be useful to combine classification codes and keywords.  For a very thorough search, every document can be reviewed within a classification code.  In this case, the more detailed CPC classification can be helpful.

When using classification codes for searching, it is important to realise that many inventions fall into several classification codes. Limiting the search to just one classification code could result in a failure to find important prior art.

Once a relevant patent document has been identified, its classification codes can give a useful insight in identifying technology areas in which to conduct further searching.  Likewise, when searching for relevant prior art against a patent document, reviewing the classification codes in the search report may help identify technology areas which were not adequately covered in the original search.

Whilst classification codes can help, it should be remembered that patent searching is a complicated process. We strongly recommend that the assistance of an experienced patent professional is sought when searching for patents and applications, particularly when considering freedom to operate.

This article is for information only and should not be treated as providing legal advice. If you require further information on patent classifications or searching, please contact our patents team.