QUDT.org is a 501(c)(3) public charity nonprofit organization founded to provide semantic specifications for units of measure, quantity kind, dimensions and data types.   QUDT is an advocate for the development and implementation of standards to quantify data expressed in RDF and JSON.   Our mission is to improve interoperability of data and the specification of information structures through industry standards for Units of Measure, Quantity Kinds, Dimensions and Data Types.

QUDT.org is a member of the World Wide Web Consortium (W3C)

QUDT.org operates thanks to volunteers, but we do have infrastructural costs of course. If you value the QUDT ontologies as a resource available to all, please consider a DONATION of any amount (tax deductible in the USA). That will allow us to keep going and growing.

Why QUDT.org

QUDT.org exists to make the QUDT Ontologies, derived models and vocabularies available to the public. Originally, QUDT models were developed for the NASA Exploration Initiatives Ontology Models (NExIOM) project, a Constellation Program initiative at the AMES Research Center (ARC).

Use Cases Benefitting From QUDT

QUDT is more than a set of vocabularies representing the various quantity and unit standards. It can be used to solve problems. Some of the associated use cases are itemized below:

  • Conversion between single and complex unit types
  • Dimensional analysis of equations
  • Finding out equivalent units in different systems of units
  • Finding out equivalent quantity kinds in different systems of quantities

Current Activities

July 1, 2020

We are excited to announce a powerful new way to browse, explore and SPARQL-query the QUDT ontology and vocabularies, using the state-of-the-art EDG environment from TopQuadrant. Please click here to check it out! There is also an introductory video to help you get started.

December 2, 2019

Release 2.1 of QUDT is now officially an open-source model and vocabulary set, hosted on our Github repository. It has ontologies for Units of Measure, Quantity Kinds, Dimensions and Types, available under a Creative Commons Attribution 4.0 International License (CC BY 4.0). Attribution should be made to QUDT.org.   Our catalog can also be found at QUDT Catalog Release 2.1. With this release, we have consolidated the unit and quantity kind vocabularies so that specific instances are easier to find, but there is still much more to do. The QUDT units vocabulary is being enhanced with the IEC 61360, UN/ECE, and UCUM unit codes for cross compatibility. Please consider joining our activity, or contributing some financial support via the "Sponsor" button on the Github repository. Note that QUDT Catalog Release 2.0 is still available for reference.

Version 1.1 of the QUDT ontologies may be downloaded from the QUDT Catalog Release 1.1, which can also be accessed from LinkedModel.org.   The catalog covers many domains of units and quantities and is being published incrementally.

If you wish to participate in reviewing this work please email manager at qudt.org or visit the repository.


QUDT is comprised of several linked ontologies. The core design pattern of the QUDT ontology is shown here:

The table below provides the Base URIs for these ontologies.

OntologyBase URI
Main QUDT Ontologyhttp://www.qudt.org/2.1/schema/qudt
QUDT Datatype Ontologyhttp://www.qudt.org/2.1/schema/datatype
QUDT Units Vocabularyhttp://www.qudt.org/2.1/vocab/unit
QUDT QuantityKinds Vocabularyhttp://www.qudt.org/2.1/vocab/quantitykind
QUDT DimensionVectors Vocabularyhttp://www.qudt.org/2.1/vocab/dimensionvector


QUDT is governed by a board of directors from different organizations.