DWPI Classification System

Companies often use different names for the same invention, and additional variation may be introduced when the patent application is translated into different languages. Also some keywords can appear in many different contexts within patent titles. For example the word "valve" can be either mechanical or electrical. So a subject classification system is essential for effective patent searching.

DWPI categorizes patent documents using a simple classification system for all technologies. This unique classification is consistently applied to all patents by Thomson Reuters subject experts, enabling effective and precise searching in a particular area of technology. Patents are divided into three broad areas: Chemical, Engineering, and Electronic and Electrical Engineering. Each of these is then further divided into Sections and Classes which describe the technical area, or areas, covered by the patent.


Patents are divided into 21 broad subject areas or Sections. These are designated A-M (Chemical); P-Q (Engineering); and S-X (Electronic and Electrical).


These Sections are then further subdivided into classes. Each Class consists of the Section letter, followed by two digits. For example X22 is the Class designation for Automotive Electrics and C04 is the Class for all Chemical Fertilisers.

When used in combination with other online search terms e.g. a Keyword Search, these Classes allow you to precisely and effectively restrict your search to the relevant subject area.

For example, the otherwise ambiguous word "WARN" can be combined with X22 (Automotive Electrics) to retrieve only those references to automotive warning devices.

DWPI cross-classifies entries to ensure that all the patents of interest are retrieved when searching.

International Patent Classification

The International Patent Classification (IPC) is an internationally recognised classification system, which is controlled by the World Intellectual Property Organisation (WIPO) and assigned to patent documents by Patent Offices. Further details are available on the WIPO web site at http://classifications.wipo.int/

Where possible we indicated next to the Class the equivalent IPC in an abbreviated form (eg A47, F23-5). However, this should only be taken as a guide, since there are areas where the DWPI Classes are assigned intellectually by our subject experts, and no strict correspondence is claimed.

In Sections P and Q (Engineering) the correlation between the IPC and Class is exact.

Prior to the introduction of the separate Electronic and Electrical Classification (Sections S-X), in 1980, a direct conversion of the IPC to the Class (Section R) was used. Reference to these R Classes may be seen online, but can be ignored since all records have been converted to the S-X series.

Patent Families

DWPI assembles information describing a patent family, starting with the new invention (Basic patent) and adding information about patents for the same invention issued in other countries (Equivalents).

Equivalent patent documents are regarded as falling within the same Classification Sections as the basic document which DWPI first classifies, except in the Engineering Sections when it may be revised if the IPC changes.

For further information on becoming a DWPI subscriber or benefiting from the DWPI Online Service simply contact your local Thomson Reuters office.



Chemical patents currently covered by DWPI are selected for inclusion in one or more of the following twelve sections. All patents with the following IPCs are guaranteed to be included in the Chemical Patents Section: A01N, A21- A23, A61K, B01, B29, C, D, G21.

A - Polymers and Plastics
B- Pharmaceuticals
C - Agricultural Chemicals
D - Food, Detergents, Water Treatment and Biotechnology
E - General Chemicals
F - Textiles and Paper-Making
G - Printing, Coating, Photographic
H - Petroleum
J - Chemical Engineering
K - Nucleonics, Explosives and Protection
L - Refractories, Ceramics, Cement and Electro(in)organics
M - Metallurgy
N - Catalysts


These twelve Sections are sub-divided down into 138 well-defined Classes. These are primarily intended to break down the subject matter simply and unambiguously for greater search precision.

Classification covers the complete patent document taking into account all the claims, particularly references to the use of chemicals or polymers, even when the main subject matter is non-chemical.

Where any patent specification falls logically into more than one section of the Chemical Classification it will be included in each of these Sections. Thus a patent involving a new dyestuff for polymeric fibres will be included in the appropriate classes of Sections A, E and F.



Engineering patents currently covered by DWPI are selected for inclusion in one or more of the following 15 sections based upon the International Patents Classification (IPC) shown in brackets.

P - General
P1 Agriculture, Food, Tobacco (A01 excluding N, A24).
P2 Personal, Domestic (A41-A47).
P3 Health, Amusement (A61-A63, excluding A61K).
P4 Separating, Mixing (B02-B09).
P5 Shaping Metal (B21-B23).
P6 Shaping Non-metal (B24-B28).
P7 Pressing, Printing (B30- B32, B41-B44).
P8 Optics, Photography; General (G02, G03, G09, G10).

Q - Mechanical
Q1 Vehicles in General (B60).
Q2 Special Vehicles (B61-B64).
Q3 Conveying, Packaging, Storing (B65-B68).
Q4 Buildings, Construction (E).
Q5 Engines, Pumps (F01-F15)
Q6 Engineering Elements (F16-17).
Q7 Lighting, Heating (F21-F28, F41-F42).


These 15 Sections are broken down into 103 finer IPC-based Classes so as to narrow the subject matter into finer profiles for greater precision. Classification is made automatically by computer, based on the IPCs on the specification or, where not present, on DWPI-assigned IPCs.

Where a patent falls into more than one of the Sections P or Q, it will be placed in each, and may also occur in one or more of the Chemical Sections A-M or Electronic and Electrical Sections S-X.

Unlike the Chemical Classification, an equivalent may introduce a fresh P or Q Class (which is then added to the master record) if it has a fresh IPC which is outside the range of IPCs covered by the Classes already assigned to the patent family.

Electronic and Electrical


Electrical and electronics patents covered by DWPI are selected for inclusion in one or more of the following six Sections:

S - Instrumentation, Measuring and Testing
T - Computing and Control
U - Semiconductors and Electronic Circuitry
V - Electronic Components
W - Communications
X - Electric Power Engineering


These six Sections are broken down into 50 Classes. These Classes are assigned according to the technical content as disclosed in the basic specification and take into account all the claims, particularly references to electrical applications, even when the main subject matter is chemical or mechanical in nature.

Where any patent specification falls logically into more than one Section of the Electronic and Electrical Classification it will be included in each of these Sections. Thus a patent involving a TV receiver line output transformer will be included in Classes V02 and W03 (Inductors and Transformers).

Classes are not intended to serve as a coding or retrieval tool, but to break down the subject matter simply and unambiguously into a number of profiles for greater precision.

Basic documents are selected for inclusion in the Electronic and Electrical Classification based mainly on their relevance to electronic and electrical industries. This means, for example that documents bearing the following IPCs are normally included: A61N, B60L, B60M, G01, G02F, G03G, G04, G05 (not G05G), G06, G07, G08, G09G, G10H, G11, G12, G21B and all IPC H.

In addition, we select from all other basics and include those of relevance to the electrical/electronic industries irrespective of assigned IPC.

All equivalents are regarded as falling within the same classes of Sections S-X as the parent document.

Approximate IPCs are given in brackets.