# International Classification for Standards

International Classification for Standards (ICS) is an international classification system for technical standards. It is designed to cover every economic sector and virtually every activity of humankind where technical standards may be used.
Developed and maintained by the International Organization for Standardization, the ICS is intended to be a continuous work in progress and is updated when necessary. The latest edition of the ICS can be downloaded free of charge from the ISO web site.
Anyone may submit a proposal for modifications or additions to the ICS.

## Purpose

The ICS serves as a structure for catalogues and databases of technical standards and other normative documents, and as a basis for standing-order systems for international, regional and national standards.

## Classification principles

The ICS uses an hierarchical classification, which consists of three nested levels called fields (Level 1), groups (Level 2) and sub-groups (Level 3). Each field is subdivided into groups, which are further divided into sub-groups.
All classification levels are designated by a classification code (called notation) and a title. The notation is a set of Arabic numerals.
Top-level items, which have no parent levels, use a two-digit notation, for example:
    43 ROAD VEHICLE ENGINEERING
The notations for groups and sub-groups include the parent-level notations. The example below shows a notation for Sub-Group 20 (Level 3), which belongs to Group 040 (Level 2) in Field 43 (Level 1).
    43.040.20 Lighting, signaling and warning devices

### Level 1 (Fields)

A field is the first level in the International Classification for Standards. It may represent one or a combination of the following:
* A sector of the economy such as agriculture, mining, construction or the packaging industry;
* A technology such as telecommunications or food processing;
* An activity such as environment protection, safety assurance and protection of public health;
* A field of science such as mathematics or astronomy.
At present the classification includes 40 fields:
    01 Generalities, terminology, standardization, documentation
    03 Services, company organization, management and quality, administration, transport, sociology
    07 Mathematics, natural sciences
    11 Health care technology
    13 Environment, health protection, safety
    17 Metrology and measurement, physical phenomena
    19 Testing
    21 Mechanical systems and components for general use
    23 Fluid systems and components for general use
    25 Manufacturing engineering
    27 Energy and heat transfer engineering
    29 Electrical engineering
    31 Electronics
    33 Telecommunications, audio and video engineering
    35 Information technology, office machines
    37 Image technology
    39 Precision mechanics, jewelry
    43 Road vehicles engineering
    45 Railway engineering
    47 Shipbuilding and marine structures
    49 Aircraft and space vehicle engineering
    53 Materials handling equipment
    55 Packaging and distribution of goods
    59 Textile and leather technology
    61 Clothing industry
    65 Agriculture
    67 Food technology
    71 Chemical technology
    73 Mining and minerals
    75 Petroleum, and related technologies
    77 Metallurgy
    79 Wood technology
    81 Glass and ceramics industries
    83 Rubber and plastics industries
    85 Paper technology
    87 Paint and colour industries
    91 Construction materials and building
    93 Civil engineering
    95 Military engineering
    97 Domestic and commercial equipment, entertainment, sports.

### Level 2 (Groups)

The ICS second level, the group, is a subdivision of the field.

### Level 3 (Sub-Groups)

Sub-groups are used in the ICS to subdivide groups into subjects that certain to a particular aspect of the subject covered by a given group. Regardless of the subject, virtually all groups include a sub-group No. 01 that covers the complete subject of the respective group. In addition, most of the groups contain a sub-group No. 99 for standards on subjects which do not correspond either to the subjects of the general sub-groups or to the subjects of the specific sub-groups of the respective groups.

### Level 4 (Units)

Level 4 subdivisions are not part of the official ICS document. The ICS rules however allow users of the classification system to subdivide the official ICS sub-groups into so-called units, making them a Level 4 component of the International Classification for Standards. This is accomplished by adding a two-digit number to the notation of the sub-group being subdivided. However, instead of a period, new notations use a hyphen as a separator. For example:
    35.220.20-10 Magnetic tapes

## Statistics

* The International Classification for Standards has 99 top-level divisions of which only 40 are presently used. The remaining 59 divisions are reserved for topics that are not yet known.
* There are three "official" levels in the ICS system, each holding ninety nine (99), nine hundred and ninety nine (999) and ninety nine (99) subsets, respectively.
* Each field of the ICS is designed to hold a maximum of 999 groups.
* Although any group in the ICS may contain no more than 99 "official" sub-groups, the holding capacity of the group can be expanded 99 times by using "unofficial" Level 4 subdivisions, an option that is built into the ICS. Adding Level 4 subdivisions to all sub-groups within a group increases the group's holding capacity to 9 801 subjects.
* The expanded version of the International Classification for Standards is capable of covering nearly 1 billion subjects (969,328,701 to be exact). This can be achieved without any restructuring of its numerical coding system. Since there are currently about 780 000 national standards in the world, the number of subjects that the ICS can offer for classification purposes exceeds 1 200 times the total number of documents that are available for classification.