IP Subnet / CIDR Calculator
Enter an IPv4 address with CIDR prefix length to instantly calculate network address, broadcast, host range, subnet mask, wildcard mask, and total hosts.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network mask as a single string like 192.168.1.0/24. The number after the slash is the prefix length — how many bits are used for the network portion. A /24 means 24 network bits and 8 host bits, giving 256 addresses (254 usable).
How to read the results
The Network Address is the first address in the subnet (unusable). The Broadcast Address is the last (also unusable). Host Range shows the first and last addresses available for assignment. Total Hosts is 2^(32-prefix) minus 2 (network and broadcast).
What are RFC 1918 private address ranges?
Three address blocks are reserved for private networks: 10.0.0.0/8 (Class A, ~16 million hosts), 172.16.0.0/12 (Class B, ~1 million hosts), and 192.168.0.0/16 (Class C, 65,534 hosts). These are not routable on the public internet.
What does /30 mean?
A /30 subnet has 4 addresses total, 2 usable hosts. It is the smallest practical subnet and is commonly used for point-to-point links between routers where only two IPs are needed.
How is the subnet mask calculated?
The subnet mask has all network bits set to 1 and all host bits set to 0. For /24, the binary mask is 11111111.11111111.11111111.00000000 = 255.255.255.0. The wildcard mask is the bitwise inverse: 0.0.0.255.