CAS Numbers – search engine

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CAS Numbers

CAS number

A CAS number is a numerical designation assigned to chemical substances by the U.S. Chemical Abstracts Service (CAS). Each individual number enables the unequivocal identification of a substance. It is one of the most common methods used in the world.

The Chemical Abstracts Service is a department of the American Chemical Society and it maintains a database of chemical compounds and sequences. At the moment, the CAS database contains over 55 million different chemical compounds, both inorganic and organic. Every entry to the CAS database is identified based on the CAS register, or CAS number for short.


Formerly chemical substances were identified mainly by means of a wide range of synonyms. However, they often proved to be unclear, as the names were constructed following local conventions, which referred to the structure, origin or chemical formula. That is why some of the well-known substances may bear numerous historical, generic or commercial names.

CAS numbers were created with simplicity and regularity in mind, so that they are easily searchable in databases. It is a reliable, international designation assigned to the specific substance in different nomenclatures and disciplines, approved by the sciences, industry and regulatory bodies.

CAS number format and manner of assignation

The format of CAS numbers is as follows: xxxxxxx-yy-z and may contain up to 10 digits. These are three digit sequences separated by hyphens. The first sequence can range from two to seven digits, the second one always has only two digits, and the third sequence comprises of a single digit.

The last digit is known as the control sum, which is a digit obtained following a special algorithm, ensuring data integrity. In the case of the CAS number, the control sum is obtained by summing the product of the first digit multiplied by 1, the second to last digit multiplied by 2, the third to last digit multiplied by 3 etc. (depending on the number of digits in the designation). From that sum, the modulo 10 is determined thus obtaining the final CAS number digit.

We can see this by using water as an example, whose CAS number is: 7732-18-5.

The first and second segment of the CAS number do not have any special meaning. They increase with the addition of subsequent substances to the register.

What is a CAS number for?

A CAS number is assigned to chemical compounds for the purpose of their identification. However, it should be remembered that it is just a designation, and not the product’s unique character. An example of this is the different anhydrous forms of citric acid, which are labelled with the same CAS number, although compounds with different hydration levels can feature other numbers. The assigned number may also aid in distinguishing stereoisomers of the given compound. Glucose has two forms: L-glucose and D-glucose (dextrose). L-glucose, with CAS number 921-60-8, is a mirror reflection of D-glucose, with the CAS number 50-99-7.

CAS number search engine

CAS number is one of the most popular methods of searching substances. With the use of this designation, one can be certain what the chemical compound in question is. Free databases are available, where via the CAS number the name, structure or molecular formula of the given substance can be found, or vice versa.

The products in the PCC Group’s portfolio also have CAS numbers assigned to the chemicals they contain. Therefore, in order to meet the demand expressed by the customers, the Product Portal has been adapted to the functionality of a CAS number browser. A specialised database has been created, containing the numbers assigned to all the products. Each of them contains the basic information about a chemical compound. It is also possible to view the structural and molecular formula. Thanks to the CAS number browser, PCC Group customers can easily find the chemical substances that meet their requirements.

FAQ - Q&A on CAS number

What is a CAS no.?
The CAS no. is assigned by the American Chemical Abstracts Service and is a type of an index identifying chemical substances. Each compound has an individual code that allows for its easy classification. Some varieties of the same substance have one CAS no., e.g. products with different concentrations or contamination degree. The CAS database contains information about organic and inorganic compounds, reactants, isotopes, minerals, alloys, etc.
How are CAS no. assigned?
For a new substance, the process of CAS number assignment begins with a submission to the Chemical Abstracts Service. The organization analyses the compound based on the data provided. At this stage, the properties of the submitted product, its structure and other data are reviewed. After the review, a unique CAS no. is assigned and entered into the CAS database. In case of additional modifications, existing items are updated.
What is the structure of CAS no.?
The CAS code consists of several parts – the initial digits constitute a prefix that is used for many substances, although not in every case. Its presence makes it easier to group similar groups of compounds. This part usually contains 2-7 digits. Individual identification elements are separated by dashes. The next part is a unique number, specific for a given compound. The last digit is calculated by a specific algorithm and is known as the check digit.
Are CAS no. globally uniform?
Yes, the CAS number is globally uniform and unique for each registered substance. The consistency of the CAS database is critical for the identification of chemical compounds for scientific and technical purposes, as well as for the safety of humans and the environment.
Do all chemicals have CAS no.?
Not all chemical substances have a CAS number assigned, but the vast majority of them do. In areas where detailed classification of compounds is important, e.g. toxicology, pharmacology, industrial chemistry, a CAS number is assigned to and used for almost every substance used therein.
Can CAS no. change?
Once assigned, the CAS number remains unchanged and is used in every case. Exceptions are possible in situations where an error has been made when entering a new substance.
How to find the CAS no. for a given chemical?
Information about any chemical can be found on the European Chemicals Agency (ECHA) website at: The PCC Group Product Portal contains a list of many popular chemicals grouped based on their CAS nos. All products offered by the PCC Group have been described in detail and classified.
Are CAS nos. required in safety data sheets (SDS) and chemical labelling?
Safety data sheets require CAS nos. to standardise the data and facilitate substance identification. Often product labels also include CAS no.
Besides CAS nos., what other chemical identifiers are used?
CAS is one of the most popular identification systems used internationally. Nevertheless, there are also other types of classification of the same compounds, e.g. UN, FEMA, EINECS, HMIS/NFPA, GHS/CLP, SMILES numbers. They are used depending on the need and purpose.
Does the CAS no. provide other information about the properties of chemicals?
The CAS system provides information on some physical and chemical properties but does not provide comprehensive data about a given chemical compound. To obtain data on specific product characteristics, you should use other available databases that are also based on CAS, e.g. PubChem, ChemiSpider, REACH regulations or chemical guides.
Why are CAS no. important?
The use of CAS no. is of great importance in the identification and classification of chemical compounds. It is particularly important when creating product dossier, as well as for safe storage, processing and transportation. The global universality of the CAS system facilitates work and communication in many areas.
Can you search for chemicals by CAS nos.?
The CAS no. is used, among others, to find detailed information about a given chemical substance easily and quickly. Based on the CAS no., you can easily search for compounds in various databases, catalogues, publications and documentation.

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CAS number infographic