Enter an IPv4 address with a prefix, such as 192.168.1.10/24, and get the network and broadcast addresses, the usable host range, the subnet mask and the total host count. The prefix length says how many leading bits are fixed as the network portion; the remaining bits identify individual hosts.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address together with a slash and a prefix length (e.g. 192.168.1.0/24). The prefix length indicates how many leading bits of the address are fixed as the network portion, while the remaining bits identify individual hosts within that network.
How to use the CIDR calculator
- Enter an IP/CIDR — type an IPv4 address that includes a prefix (e.g. 192.168.1.10/24).
- Calculate — press the button.
- Read the results — the network and broadcast addresses, the subnet and wildcard masks, and the usable host range and count appear instantly.
What are the network and broadcast addresses?
The network address is the first address in the range and identifies the subnet itself; the broadcast address is the last address and is reserved for sending to every host on the subnet at once. Neither can be assigned to a device, so both are excluded from the usable hosts — except for /31 (point-to-point links) and /32 (a single host).
How are the subnet mask and prefix length related?
The prefix length equals the number of bits set to 1 in the subnet mask. For example, /24 corresponds to 255.255.255.0 and /16 to 255.255.0.0. The longer the prefix, the larger the network portion and the fewer hosts you can use.
How many hosts are in a /24 network?
A /24 has 256 total addresses, of which 254 can be assigned to hosts after subtracting the network and broadcast addresses. In general, the number of usable hosts is 2^(32−prefix) − 2 (except for /31 and /32).
Where is CIDR used?
It's widely used for subnetting a network into the sizes you want, route aggregation, specifying IP ranges in firewall and access-control rules, and designing address ranges for cloud VPCs.