CAS Number

Environmental LawCAS number (CAS registry numbers) is a unique numerical identifier for a chemical element, polymer, compound, biological sequence, alloy and mixture. They are also referred to as CAS numbers, CAS #s or CAS RNs.

Chemical Abstracts Service (CAS), one division of the American Chemical Society, assigns these identifiers to each chemical that has been described in the literature. The goal is to make database searches more efficient and convenient, as chemicals often have many names. Nearly all molecule databases today permit searching by CAS number.

Since September 2009, there were more than 50 million inorganic and organic substances and more than 61 million sequences found in the CAS registry. About 50,000 new numbers are added each week.

CAS also sells and maintains a database of these chemicals, which is known as the CAS registry.

A CAS registry number is separated into three parts by hyphens, the first consists of as many as 7 digits, the second consists of two digits, and the third consists of a single digit serving as the check digit. The numbers are assigned in increasing order and don’t have any inherent meaning.

The check digit is calculated by taking the last digit multiplied by 1, the next digit multiplied by 2, the next digit multiplied by 3 etc., adding all of these up and computing the sum modulo 10. For instance, the CAS number of water is 7732-18-5: the checksum 5 is then calculated as follows: (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.

Isomers, mixtures, and enzymes

Different stereoisomers of a molecule are given different CAS numbers: L-glucose has 921-60-8, D-glucose has 50-99-7, α-D-glucose has 26655-34-5, etc. Occasionally, whole classes of molecules will receive a single CAS number: the group of alcohol dehydrogenases has 9031-72-5. An instance of a mixture with a CAS number is mustard oil (8007-40-7).

CAS information is all copyrighted by the American Chemical Society. Users who wish to incorporate CAS numbers into their private databases should review the details of the CAS usage policy:

An Organization or User may include, without a license and without paying a fee, as many as 10,000 CAS Registry Numbers or CASRNs in a website, catalog, or other product for which there is not any charge

CAS REGISTRY is the most authoritative collection of information regarding disclosed chemical substances. It contains more than 51 million inorganic and organic substances and 61 million sequences.

CAS REGISTRY covers substances that have been identified from the scientific literature from 1957 up to the present, with additional substances dating back to the early 1900s

Every CAS Registry Number (frequently referred to as a CAS Number):