Is the CAS number the same as the MSDS number?

There isn’t one, but two distinct numbers on a Safety Data Sheet for hazardous chemical identification. Those are the CAS registration number and the SDS ID number (formerly known as the MSDS number). These numbers are not interchangeable! Sometimes these can be mistaken for each other, but in fact they serve very different purposes and have differing formats:

CAS Registration Number

This number is a unique identifier for hazardous substances. The number itself does not have any significance to the chemical, but rather provides a way of identifying a certain chemical substance that goes by many different names. It must also be noted that CAS registration numbers are not typically assigned to specific mixtures as those often have multiple dangerous chemical substances, therefore each requiring their own CAS number. Take for example an ammonia in carbon dioxide mixture. Under section three, there are CAS numbers assigned to both ammonia and carbon dioxide.

A CASRN is a string of up to ten digits separated into three parts. The first section can hold between two and seven numbers followed by a hyphen, the second section must have two digits, and one more hyphened section has only one number to serve as a check. There are up to one billion different combinations for CAS numbers and their corresponding chemical substances. Right now, there are only around 182 million that have been assigned a CAS number, so there is a lot of room to grow.


An SDS ID is an eight-digit number located at the top right corner of every page in the Safety Data Sheet provided by the manufacturer. Employees can then easily look up the chemical and find the SDS ID number it pertains to, which will lead them to where the file is stored. Unlike CAS numbers, the SDS ID is used for every chemical substance and chemical mixture!

Both the CAS number and the SDS ID serve important roles in the hazard communication standard/GHS. That being the correct identification of hazardous materials, which ultimately helps prevent accidents and emergency situations.


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