Documentation Registry

Sources & Reference Documents

Below is a complete record of the primary standards, publications, and treaties from which our conversion factors are derived.

Important Notice Regarding References & Endorsement

The organizations, treaties, and standard documents listed below are cited solely as the factual and legal basis for our mathematical conversion constants. These organizations do not sponsor, certify, review, or endorse this website.

International Bureau of Weights and Measures (BIPM)

The International System of Units (SI Brochure, 9th edition, 2019)

External Resource

Relevant Units / Definitions: Meter (m), Kilogram (kg), Second (s), Kelvin (K), Liter (L), Hectare (ha)

Reference Summary: Primary global reference for the definitions of SI base units and derived units, including the 2019 redefinition of the kilogram based on the Planck constant.

National Institute of Standards and Technology (NIST)

NIST Special Publication 811: Guide for the Use of the International System of Units

External Resource

Relevant Units / Definitions: Yard (yd), Foot (ft), Inch (in), Mile (mi), Pound (lb), Ounce (oz), Square Foot (ft²)

Reference Summary: Authoritative US government reference providing exact conversion factors between customary units and the SI system.

National Institute of Standards and Technology (NIST)

NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices

External Resource

Relevant Units / Definitions: US Liquid Gallon, US Fluid Ounce, US Cup, Short Ton, Acre

Reference Summary: Defines commercial legal measurement standards in the United States, including the US liquid gallon (exactly 231 cubic inches).

International Standards Agreement (US, UK, CA, AU, NZ, ZA)

International Yard and Pound Agreement of 1959

External Resource

Relevant Units / Definitions: Yard (0.9144 m exact), Avoirdupois Pound (0.45359237 kg exact)

Reference Summary: The multilateral treaty establishing unified international definitions for the yard and the avoirdupois pound across English-speaking nations.

Parliament of the United Kingdom

Weights and Measures Act 1985 (Schedule 1)

External Resource

Relevant Units / Definitions: Imperial Gallon (4.54609 L exact), Imperial Fluid Ounce, Imperial Long Ton

Reference Summary: Statutory legal definition of UK imperial units, establishing the Imperial Gallon as exactly 4.54609 cubic decimetres (litres).

International Organization for Standardization (ISO)

ISO 80000-3: Quantities and Units — Space and Time

External Resource

Relevant Units / Definitions: Kilometer per Hour (km/h), Meter per Second (m/s), Standard Time Intervals

Reference Summary: International standard specifying names, symbols, and definitions for quantities and units of space and time.

International Hydrographic Organization (IHO)

First International Extraordinary Hydrographic Conference (1929)

External Resource

Relevant Units / Definitions: Nautical Mile (1,852 m exact), Knot (nmi/h)

Reference Summary: Adopted the international nautical mile as exactly 1,852 meters, widely used in aviation and maritime navigation.