Standards are indexed in their respective databases using descriptive fields.  These fields contain the following:

• Basic identifiers known as "designations" (the standard's "number"), including alpha characters and numbers;
• Content information including title and abstract;
• Subject information including various classification codes; and
• Status including whether the standard is published, under development, withdrawn or superseded.

Ironically, there is not a standard method of numbering standards that cuts across all standards bodies.  However, there are similarities among them: most standard designations include a number that is assigned serially at the time of issue.  Some also include meaningful elements such as prefixes that help with classification of the standard.  Some of the major designation schemes are below:

ISO

• Format: ISO[/IEC][/ASTM] [AA] #####-##:YYYY Title 
• if the standard is jointly developed with IEC or ASTM, these are noted as shown in the designation
• numbers (sometimes blocks of numbers) are sequentially assigned to documents; if the document is a technical report, technical specification, or guide, the letters "TR," "TS," or "Guide" precede the numbers
• the subpart is indicated by a numeral following a dash
• the year of the standard is indicated by a date following a colon
• the title of the standard is descriptive of its content

ASTM

• Format: ASTM A####-YY(YYYY) Title
• First letter indicates the general category of the item covered in the standard
  • A - Ferrous metals and products
  • B - Nonferrous metals and products
  • C - Cementitious, ceramic, concrete, and masonry materials
  • D - Miscellaneous materials and products
  • E - Miscellaneous subjects
  • F - End-use materials and products
  • G - Corrosion, deterioration, weathering, durability, and degradation of materials and products
• Numbers following the first letter are sequentially assigned
• The numbers following the dash indicate the last revision date; the year in parentheses is a reapproval date
• The title of the standard includes its type (e.g., "guide") and describes the subject

ANSI 

• ANSI does not generate standards per se, but rather will review and adopt standards that meet their criteria
• Format: ANSI [Identifier from the original standards organization]

Occasionally, multiple standards organizations may have shared (dual reference) standards - these are typically denoted by multiple organizational acronyms in the standard title. If multiple versions of a standard are active (e.g. ISO vs EN ISO) there may be small differences in the standards due to translation imperfections or regional requirements.

International Classification for Standards (ICS)

The ICS is a standard method of classification for standards created by ISO (see ISO Standard). It provides categories for all products or activities for which standards are used. By so doing, searchers have a very useful tool by which standards can be found.  

ICS Hierarchy Example

The following example illustrates the hierarchical structure of the ICS, including fields of activity, groups within each field, and subgroups within some of the groups:

• ...
• 83: Rubber and plastic industries
  • 83.020: Manufacturing processes in the rubber and plastics industries
  • 83.040: Raw materials for rubber and plastics
    • 83.040.01: Raw materials for rubber and plastics in general
    • 83.040.10: Latex and raw rubber
    • 83.040.20: Rubber compounding ingredients
    • 83.040.30: Auxiliary materials and additives for plastics
  • 83.060: Rubber
  • 83.100: Cellular materials
  • ...
• 85: Paper technology
• ...

See ISO Browse by ICS to see the structure of the ICS, or download the full listing at International Classification for Standards.

Other Methods of Classification

Other classification systems exist, which are used by individual standards organizations.  A few of these are as follows:

• Some organizations classify standards by the technical committee (TC) that oversees the standard.  One can find standards on diverse subjects such as screw threads (ISO/TC 1), Chemistry (ISO/TC 47), mechanical testing of metals (ISO/TC 164), and geotechnics (ISO/TC 182) by locating the proper TC and scanning through standards in that area.
  • See ISO Browse by TC.
  • Use "Technical Committee" filter in the left-hand column of the results page for the ASTM Standards & Engineering Digital Library.
• Often standards can be narrowed to a specific industry sector  (e.g., electronics, energy & utilities).
  • Industry classification categories and codes can be found at the NAICS & SIC Identification Tools website. 
• In addition to TC and ICS classifications, the ASTM search engine uses internal classifications by category (e.g., materials, processes) and topic (e.g. fatigue and fracture mechanics, sports safety).
  • Search ASTM Standards & Engineering Digital Library and look at these filters in the left-hand column of the results page.