What this tool does
The CIDR Calculator passes an IPv4 address and network prefix to a shared unsigned 32-bit calculation engine to determine the entire CIDR block containing that address. You can paste a complete CIDR into the IP field or enter the prefix separately.
- The full prefix range from /0 through /32 is supported.
- /31 shows two usable addresses under RFC 3021 point-to-point link semantics; /32 shows a single host route.
- Address counts are calculated from the boundaries; the tool does not enumerate every IP address in a large network.
How to use it
- Enter an IPv4 address or a complete IPv4/CIDR block.
- If you did not paste a complete CIDR block, enter the prefix separately.
- Click Calculate CIDR.
- Review the subnet mask, network and broadcast addresses, range, and address-count details.
How it works
A /n prefix means that the first n high-order bits are contiguous network bits. Network Address = IP AND Subnet Mask; Broadcast Address = Network OR Wildcard Mask; the total address count is 2^(32-n).
Examples
- 192.168.1.100/24 → Network 192.168.1.0, Broadcast 192.168.1.255, 256 addresses total.
- 192.168.1.10/31 → Range 192.168.1.10–192.168.1.11, with two usable point-to-point addresses under RFC 3021.
- 192.168.1.10/32 → Network and broadcast are both that address, for one host route in total.
Common uses
- Determine which CIDR block contains an address.
- Convert a prefix to a subnet mask and wildcard mask.
- Plan network boundaries and verify address counts.
Privacy
Inputs and results are processed only in local browser memory. Nothing is uploaded, sent to an online API, or stored automatically.
CIDR Calculator Features
Calculate the subnet mask, network and broadcast addresses, address range, and host counts from an IPv4 address and CIDR prefix. Useful for network planning, configuration checks, and troubleshooting; results can be reviewed and copied immediately.
FAQ
What does /24 mean in CIDR notation?
/24 designates the first 24 bits as network bits and the remaining 8 as host bits, for 256 total addresses.
How many IP addresses are in a /24?
There are 256 total addresses. In the traditional network and broadcast model, 254 are typically considered usable host addresses.
How are a subnet mask and CIDR related?
A CIDR prefix is the number of consecutive leading 1 bits; for example, /24 corresponds to 255.255.255.0.
Why is /31 a special case?
RFC 3021 allows both addresses in a /31 to be used on a point-to-point link, so the usual total-minus-two rule does not apply.