Check digit verification of CAS Registry numbers
A CAS Registry Number® includes up to 10 digits which are separated into 3 groups by hyphens. The first part of the number, starting from the left, has 2 to 7 digits; the second part has 2 digits. The final part consists of a single check digit.
The check digit is developed by following a standard calculation shown below. Use it to see if you have a valid CAS Registry Number.
![](https://cdn.prod.website-files.com/650861f00f97fe8153979335/667a35b35eb69f5784bd1fbe_checkdig_image_small3.png)