Note: This page and information contained within are still under review as of 03-26-2021

Terminology owner/maintenance organisation

Name, contact details, website

LOINC and Health Data Standards, Regenstrief Institute, Inc., Indianapolis, IN

1101 W 10th St, Indianapolis, IN 46202

Formal name of the code system

Unified Code for Units of Measure

Short name or abbreviation of the code system name

Technical identifier/s for the code system 

OID: 2.16.840.1.113883.6.8
Canonical URL:

Scope/domain statement for the code system

(Official or from HTA)

"The Unified Code for Units of Measure (UCUM) is a code system intended to include all units of measures being contemporarily used in international science, engineering, and business. The purpose is to facilitate unambiguous electronic communication of quantities together with their units. The focus is on electronic communication, as opposed to communication between humans. A typical application of The Unified Code for Units of Measure are electronic data interchange (EDI) protocols, but there is nothing that prevents it from being used in other types of machine communication."

Link to information about the code system - including how to obtain the content

The full UCUM specification is available here:

Arrangement or agreements with HL7 for use of content

From the UCUM Copyright Notice and License:

Permission is hereby granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the UCUM codes, UCUM Specification, and UCUM table (in all formats in which it is distributed by The Organization and the UCUM Organization) (collectively, the "Licensed Materials") for any commercial or non-commercial purpose, subject to the following terms and conditions..." See the IP and Licensing information for further details. 

9/2020: Regenstrief is working on updating the terms of use and will update this page when it is finalized.

Version management - timing and identification of versions9/2020: Regenstrief is working on a formal versioning plan and will update this page when it is finalized.

IP Information and Licensing Information

The UCUM codes, UCUM table (regardless of format), and UCUM Specification are copyright © 1999-2009, Regenstrief Institute, Inc. and the Unified Codes for Units of Measures (UCUM) Organization. All rights reserved.

9/2020: Regenstrief is working on updating the terms of use and will update this page when it is finalized.

HL7 users of this information - which HL7 products use this link (if known)

Process to request content change

The current process for requesting changes to UCUM is through the Trac system on the UCUM website.

Other useful Information

Information current as at (date)

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  1. Swapna Abhyankar  Please validate what I've included in this draft, and add anything I may have missed. I wasn't sure about versioning and change requests,

    Also, I noticed that the PHIN VADS page has an erroneous (i.e., different than what you have declared as the canonical URL) code system URL listed. May need to contact them to update.

  2. Thanks Caroline Macumber ! I updated some of the text and also contacted PHIN VADS.

  3. Thanks Swapna AbhyankarJessica Bota, this is good to go, please proceed on the UTG side.

    1. Caroline Macumber I'm starting the process and will post the ticket once available. Just wanted to note that there appears to be a missing colon in the URL specified above. 

      1. Fixed. the hyperlink was right, just the link text that was missing the colon.

  4. The URL that has been in production with FHIR since FHIR was first published is  This is tied to normative content in FHIR and is used everywhere.  Making a change at this point is going to cause incredible grief.  The choice of URL was made with full discussion with Regenstrief at the time.  This is NOT something that can be changed.  

    1. HI Llyod - As far as I understand the current agreements and process between Vocab/UTG/HTA/FHIR...the existing URL will still remain and be valid, no change is required to published normative content in FHIR. The URL from the publishing authority will be added to the UTG NamingSystem.

      Ted Klein

      1. Someone sending the new URL in FHIR would be non-conformant.  Having the 'preferred' URL be non-conformant is not exactly a great thing.  Why would the HTA accept a change to the URL at all?  We need to stress the impact on the implementer community over preference of the organization responsible for the code system.

        1. Systems must design for use of namingsystem. That is the outcome of adopting meaningful identifiers. 

          1. NamingSystem is about conversion from CDA and other external sources.  It does NOT mean that implementations need to worry about URLs changing in production.  Once we establish a URL as the official URL for code system/identifier system, that should never change.  And certainly we don't break existing implementations because the organization who is responsible for the code system/identifier system "prefers" it.  Changes like this mean industry costs in the hundreds of thousands or millions of dollars.  It's not something we can just "Do" because NamingSystem exists.

            1. All.  We have just gone through the Equinox for another year; wherever we are in the world, the seasons are changing in some way.  Change is a fundamental reality and we ignore it at our peril.  If somehow we have constructed something that is unable to cope sensibly (and therefore expensively) with change, we have been foolish.  Better to face it and deal with it before it breaks us. 

              We (the HTA) have established policies which we trust come as close as we sensibly can to the requirements (because sometimes, requirements are actually unwise as all good analysts know).  One of those policies is respect for code system owners.  This policy costs nothing; please all involved in this conversation, abide by it.

              I shall also post this on the Zulip chat, because I am aware that for some folk, that medium is their only medium for information.  Apologies therefore if you receive this twice, but maybe that too has value.

              1. Hi Julie, I've just been looking through the pages here looking for a policy that applies to requests for CodeSystem URI changes and have come up empty :-(

                The best I've been able to find relates to the JIRA process and the pre-existence of URIs already in use.

                I have not found anything that addresses Lloyd McKenzie's issues around assessing the cost of change?

                1. Hello Michael.  The policy is Policy on Maintenance of External Code System Identifiers (URIs) here and on the child pages.  I too have not been offered any evidence of "cost of changes" although it is being thrown around a lot.  If you or anyone else can quantify the "costs" that are being used as the block to manage change, it would be very helpful.  Common sense and one's own experience knows that re-work has cost, of course, but not necessarily the scale of that cost. 
                  The Agile approach which is founded on a principle of allowing re-work in order to be successful somehow also becomes somewhat reluctant to do re-working...seems a little odd, doesn't it   

  5. Confirming that remains valid - it redirects to

  6. Lloyd McKenzie , this was not an arbitrary change that we made out of preference for one URL over another.

    Until last month, the unitsofmeasure site had been maintained outside of the purview of Regenstrief. Maintenance was intermittent, and for the last several years no updates had been made, spam was out of control, and the site would often be down. Requests for new units and updates to existing information had not been addressed.

    Regenstrief took over maintenance of the specification in order to resolve these issues and maintain the standard. The circumstances were such that we had to create a new site. We would have preferred to update the existing site but that was not possible.

    I know it's not ideal, but at least moving forward it will be stable and the standard will be maintained.

    1. To clarify, do you mean that Regenstrief no longer has control over the domain and thus the content hosted there is incorrect?  

    2. This confuses 2 different matters. We have no issue with the web site being - I like that. This has to do with FHIR implementations using as the canonical URL. If they are allowed to do that 0- which is necessary - then that remains the canonical URL, even if it's not the web site, and this page should say so

      1. I agree with Grahame's point (existing implementations can continue to use the established URL) but perhaps wrongly assumed that the intergration of UTG has matured to the point where utilization of UTG and the available naming system entries would support verification of the the alternate URL provided by the SDO. All of this however was predicated on balancing Vocab's policy statement that the SDO owns the IP around their Code System identifier here with the reality of implementers plight for consistency. This devisive topic was discussed at today's HTA WGM meeting and at Vocab's meeting on Monday 9/21/2020 (minutes here) and it was agreed that Vocab would seek legal clarity from HL7 HQ with regard to the IP ownership/rights of the identifiers.  In the meantime, the URL registration for UCUM is on hold amd the related Vocab policy has been flagged as "under review".  HTA and/or Vocab will make sure to document and communicate progress with the HL7 community via zulip.

      2. It doesn't help that people keep saying URL when they're actually talking about a URI.  (If I had a $1 for every FHIR discussion that mixed these up :-)

  7. Regenstrief never had control over the domain.

  8. Caroline Macumber , let's put the URL update on hold while we try to get ownership of I'll keep you posted.