About the CIDR Calculator
The IPv4 CIDR calculator converts an address and prefix length into the boundaries and masks of its network. It performs the math in your browser and is useful when planning subnets, checking firewall ranges, or learning how CIDR notation divides IPv4 space.
How to use this tool
Enter an IPv4 address with a prefix such as 192.168.1.20/24. The host portion does not need to be zero; the calculator derives the containing network. Run the calculation to view the network address, broadcast address, subnet and wildcard masks, first and last addresses, and capacity. Treat /31 and /32 networks according to the protocol and device you are configuring, since their usable-address conventions differ from traditional multi-host subnets.
How to read the result
The prefix length is the number of leading network bits. A larger prefix creates a smaller block: /24 contains 256 total addresses, while /25 contains 128. The network address is the first address in the block and the broadcast address is the last for conventional IPv4 subnetting. The subnet mask expresses network bits as dotted decimal, while the wildcard mask is its inverse and is often used in access-control syntax.
Limits and privacy
This calculator handles IPv4 only and uses unsigned 32-bit arithmetic locally in the tab. It does not validate whether a range is publicly routable, assigned to your organization, or appropriate for a particular vendor. Host-capacity rules depend on context, especially point-to-point /31 networks and single-host /32 routes. No entered CIDR value is sent to buffer.lol.
Common questions
- Can I enter a host address instead of the network address?
- Yes. The calculator uses the prefix to find the containing network and its boundaries.
- Why are /31 and /32 networks special?
- A /31 can be used on point-to-point links without traditional network and broadcast reservations, while a /32 identifies one IPv4 address.