Subnet Calculator
Enter an IP address and CIDR prefix or subnet mask to calculate network details
Results
Summary
CIDR range: 192.168.1.0 – 192.168.1.255
Binary breakdown— dark = network bits, light = host bits
How subnetting works
Network address
The first address in a subnet — all host bits set to 0. Identifies the subnet itself, not assignable to a device.
Broadcast address
The last address in a subnet — all host bits set to 1. Sent to all devices in the subnet, not assignable to a device.
First usable host
Network address + 1. The first IP address that can be assigned to a device.
Last usable host
Broadcast address − 1. The last IP address that can be assigned to a device.
Wildcard mask
The inverse of the subnet mask (255 minus each octet). Used in Cisco ACLs, OSPF network statements, and BGP prefix lists.
Usable hosts
2^(32 − prefix) − 2. Subtract 2 because the network and broadcast addresses are reserved.
Frequently asked questions
What is a subnet mask?
A subnet mask is a 32-bit number that divides an IP address into a network portion and a host portion. The network bits are all 1s, the host bits are all 0s. For example, 255.255.255.0 (/24) means the first 24 bits identify the network.
How do I find the network address?
Perform a bitwise AND between the IP address and the subnet mask. The result is the network address. For example: 192.168.1.100 AND 255.255.255.0 = 192.168.1.0.
How do I find the broadcast address?
Set all host bits to 1. The easiest way: take the network address and OR it with the wildcard mask (the inverse of the subnet mask). For a /24 network, the broadcast is the network address with the last octet set to 255.
How many usable hosts does a /24 subnet have?
A /24 subnet has 2^8 = 256 addresses. Subtract 2 (network address and broadcast) = 254 usable hosts. The formula is 2^(32-prefix) - 2 for any prefix length.
What is the wildcard mask?
The wildcard mask is the bitwise inverse of the subnet mask. It is used in Cisco ACLs and OSPF network statements. For 255.255.255.0, the wildcard is 0.0.0.255.