A specification is an explicit set of requirements to be satisfied by a material, product, or service.

Use

In engineering, manufacturing, and business, it is vital for suppliers, purchasers, and users of materials, products, or services to understand and agree upon all requirements. A specification is a type of a standard which is often referenced by a contract or procurement document. It provides the necessary details about the specific requirements.

Specifications may be written by government agencies, standards organizations (ASTM, ISO, CEN, etc), trade associations, corporations, and others.

A product specification does not necessarily prove the product to be correct. Just because an item is stamped with a specification number does not, by itself, indicate that the item is fit for any particular use. The people who use the item (engineers, trade unions, etc) or specify the item (building codes, government, industry, etc) have the responsibility to consider the available specifications, specify the correct one, enforce compliance, and use the item correctly. Validation of suitability is necessary.

An example of a US Federal specification is FIPS-PUB 159, Detail Specification for 62.5-μm Core Diameter/125-μm Cladding Diameter Class Ia Multimode Optical Fibers. (Source: from Federal Standard 1037C and from MIL-STD-188)

Content

A specification might include:

• Descriptive title and scope of the specification
• Date of last effective revision and revision designation
• Person, office, or agency responsible for questions on the specification, updates, and deviations.
• The significance or importance of the specification and its intended use.
• Terminology and definitions to clarify the meanings of the specification
• Test methods for measuring all specified characteristics
• Material requirements: physical, mechanical, electrical, chemical, etc. Targets and tolerances.
• Performance testing requirements. Targets and tolerances.
• Drawings, photographs, or technical illustrations
• Workmanship
• Certifications required.
• Safety considerations and requirements
• Environmental considerations and requirements
• Quality requirements, Sampling (statistics), inspections, acceptance criteria
• Person, office, or agency responsible for enforcement of the specification.
• Completion and delivery.
• Provisions for rejection, reinspection, rehearing, corrective measures

Process capability considerations

A good engineering specification, by itself, does not necessarily imply that all products sold to that specification actually meet the listed targets and tolerances. Actual production of any material, product, or service involves inherent variation of output. With a normal distribution, the tails of production may extend well beyond plus and minus three standard deviations from the process average.