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CIDR Calculator

Calculate IP network details from CIDR notation: network address, broadcast address, first/last usable host, subnet mask, wildcard mask, and total host count. Supports IPv4 CIDR ranges from /0 to /32.

How to Use CIDR Calculator

  1. 1Enter a CIDR notation (e.g., 192.168.1.0/24 or 10.0.0.0/8).
  2. 2The network address, broadcast address, and usable host range are calculated instantly.
  3. 3Subnet mask and wildcard mask are shown alongside the total host count.
  4. 4Use this when planning network segments, configuring firewalls, or cloud security groups.
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Frequently Asked Questions

What is CIDR notation?▾
CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network mask together. Format: {IP}/{prefix_length}. For example, 192.168.1.0/24 means: the IP is 192.168.1.0, the prefix length is 24 bits, and the subnet mask is 255.255.255.0. The /24 means the first 24 bits identify the network and the remaining 8 bits identify hosts. Common CIDR prefixes: /8 = Class A (16M hosts), /16 = Class B (65k hosts), /24 = Class C (254 hosts), /32 = single host.
What is the difference between network address, broadcast, and usable hosts?▾
In any subnet: The network address (first IP) identifies the network itself — it cannot be assigned to a device. The broadcast address (last IP) is used to send data to all hosts on the subnet — it also cannot be assigned. Usable hosts = total IPs − 2 (minus network and broadcast). For /24: total 256 IPs, 254 usable. Exception: /31 networks (2 IPs, used for point-to-point links) and /32 (single host) have no traditional network/broadcast addresses per RFC 3021.
How do I calculate a subnet mask from prefix length?▾
A prefix length (e.g., /24) tells you how many leading bits are set to 1 in the subnet mask. /24 = 24 ones followed by 8 zeros in binary = 11111111.11111111.11111111.00000000 in dotted decimal = 255.255.255.0. Quick reference: /8=255.0.0.0, /16=255.255.0.0, /24=255.255.255.0, /25=255.255.255.128, /26=255.255.255.192, /27=255.255.255.224, /28=255.255.255.240, /29=255.255.255.248, /30=255.255.255.252.
What is the wildcard mask and when is it used?▾
The wildcard mask is the inverse of the subnet mask (bitwise NOT). Where subnet mask has 1, wildcard has 0, and vice versa. For 255.255.255.0 subnet mask, the wildcard is 0.0.0.255. Wildcard masks are primarily used in: (1) Cisco ACLs (access control lists) to define which IP bits matter in matching rules, (2) OSPF network statements, (3) Juniper firewall filters. In ACLs, a 0 bit means "must match" and a 1 bit means "don't care".
What are private IP address ranges?▾
RFC 1918 defines three private IP address blocks reserved for internal network use (not routable on the public internet): 10.0.0.0/8 (10.0.0.0 – 10.255.255.255, ~16.7M addresses), 172.16.0.0/12 (172.16.0.0 – 172.31.255.255, ~1M addresses), 192.168.0.0/16 (192.168.0.0 – 192.168.255.255, 65,536 addresses). These ranges are used for home networks, corporate intranets, cloud VPCs, and Kubernetes pod networks. All other IP addresses are public/routable.