CIDR Calculator

The CIDR Calculator converts between CIDR notation, subnet masks and IP address ranges. Use the tool menu at the top of the page to switch between DNS Domain Analysis, DNS Lookup, SPF Policy Test, CIDR Calculator and DKIM Generator.

Choose a mode, fill in the fields and click the button.

Mode	Fields	Result
IP Address	IP Address, CIDR	Click Check to see whether the IP address is in the range (IP Address Found or IP Address not Found).
CIDR to IP Range	CIDR	Click Calculate to see the CIDR Range, CIDR Base, Netmask, Bitmask, Host, Broadcast, Block Size, First IP and Last IP.
IP Range to CIDR	First IP Address, Last IP Address	Click Calculate to see the CIDRs that cover the range.

Note: CIDR to IP Range and IP Range to CIDR support IPv4 addresses only.

Related Topics

• SPF Policy Test — Check whether a sender IP address is authorized by a domain's SPF record.
• DNS Lookup — Look up DNS, DMARC, MTA-STS and TLS-RPT records for any domain.