Everything you need to know about CAS Numbers


What is a CAS number?

CAS Registry Numbers® or CASRNs®, commonly referred to as CAS numbers, are unique numerical identifiers assigned to chemicals by the Chemicals Abstract Service (CAS: A Division of The American Chemical Society). CAS numbers provide a simple, consistent and reliable way of identifying chemical substances so that they are recognisable regardless of your region.

Each CAS number is assigned to only one substance, ensuring that the CAS number is unique to that chemical. The number, which is assigned as soon as the chemical enters the CAS Registry® database, can be up to ten digits in length and is separated into three parts with hyphens. The first part contains two to seven digits, the second part contains two digits, and the third part consists of just one digit, known as the check digit. In their current format, there are a maximum of one billion unique CAS numbers available. They have no real chemical significance and are assigned in sequential order, so that newer substances have larger numbers than the chemicals that previously entered the registry. 

The CAS Registry®

The chemicals and their assigned CAS numbers are part of a centralised collection known as the CAS Registry®, where thousands of new chemicals are added on a daily basis, resulting in the most authoritative database of disclosed chemical substances. The CAS Registry® numbers have been assigned to every unique chemical substance described in scientific literature from 1957 to present day, as well as additional substances dating as far back as the early 1900s. 

As of 2020, the CAS Registry® contained over 159 million unique chemical substances, as well as about 70 million protein and nucleic acid sequences. In April 2021, CAS announced it had registered its 250 millionth unique chemical substance. 

Why we need CAS numbers

As CAS numbers are unique and specific to individual substances, they provide an unmistakable way of identifying chemicals no matter how they might be described. Chemical compounds can often be described in many different ways, such as by molecular formula, shipping name, systematic name and proprietary or trade names to list a few. For example, Hydrogen Peroxide and Dioxidane are in fact, the same chemical substance, but this might not be immediately obvious until we see that they share the same CAS number. From an inventory and safety viewpoint, the CAS number is an invaluable tool that quickly shows users reliable and accurate information about the chemicals they have in their possession.

The implementation of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) in 2012, meant that CAS numbers needed to be included in all Safety Data Sheets (SDS) from 1 December 2015. These CAS numbers provide an extra form of identification for the chemical, reducing the confusion caused by the many different names for one chemical and also by these chemical names being misspelled by non-chemist users and laypersons who are dealing with the chemical.

CAS numbers are recognised as a universal standard and have been embraced by scientists, and industry and regulatory agencies around the world. Nearly every chemical database in the world allows users to search for chemicals by CAS number. 

CAS numbers can sometimes be the only distinguishing feature amongst like chemicals
CAS numbers can sometimes be the only distinguishing feature amongst like chemicals

Chemwatch is here to help

Like CAS numbers, Chemwatch’s main objective is to ensure your safety by minimising risk. To avoid mishandling and misidentification, chemicals should be accurately labelled, tracked and stored. For assistance with any of these or for answers to your questions about the safety, storage and labelling of your chemicals, contact us on (03) 9573 3100 or at sales@chemwatch.net.


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