CIDR is the short for Classless Inter-Domain Routing, an IP addressing scheme that replaces the older system based on classes A, B, and C. A single IP address can be used to designate many unique IP addresses with CIDR. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP network prefix. CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations.
You may use the below IP to netmask calculator to easily translate a CIDR address into netmask format.
CIDR to Netmask
Netmask to CIDR
Add The Netmask Widget On Your Website
You can easily add the netmask widget on your website by copying the following HTML code and place it on your web page