Why subtract 2 for usable hosts?

The first address in a subnet is reserved for the network address and the last for the broadcast address, so they can't be assigned to hosts.

Hosts per Subnet Calculator

Calculate the total and usable IPv4 host addresses available for any CIDR prefix length, useful for VLSM subnetting design.

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Formula

Total Addresses = 2^(32 − CIDR), Usable = Total − 2

IP Subnetting Explained With a Real /24 Example

How network address, broadcast address, and usable host count are calculated from an IP and CIDR prefix.

Subnet Calculator

Calculate network address, broadcast address, and host range from an IP and CIDR.

Wildcard Mask Calculator

Convert a CIDR prefix length to its wildcard mask, used in ACLs.

IP to Binary Converter

Convert an IPv4 address to its binary representation.

File Transfer Time Calculator

Calculate how long a file will take to download or upload at a given speed.

Network Throughput Calculator

Calculate effective throughput accounting for protocol overhead.

Packet Loss Percentage Calculator

Calculate the percentage of network packets lost in transit.