IP Subnet Calculator

What is an IP Subnet Calculator?

An IP Subnet Calculator computes subnet details for an IPv4 address and CIDR prefix. It calculates the network address, broadcast address, subnet mask, host range, and number of usable hosts. Network administrators use it for IP planning and management.

How to calculate subnets manually (the formula)

The subnet mask is derived from the CIDR prefix: set the first n bits to 1 and the rest to 0. For /24: 255.255.255.0. The network address is the IP ANDed with the mask. The broadcast address is the network ORed with the inverted mask. Usable hosts = 2⁽³²⁻ⁿ⁾ − 2.

Example calculation

For IP 192.168.1.10/24: the subnet mask is 255.255.255.0. The network address is 192.168.1.0. The broadcast address is 192.168.1.255. Usable hosts = 2^(32−24) − 2 = 2⁸ − 2 = 254. The host range is 192.168.1.1–192.168.1.254.

Common mistakes

• Forgetting to subtract 2 for network and broadcast — In most subnets, the first address is the network ID and the last is the broadcast address. These are not usable by hosts.
• Using /31 or /32 incorrectly — A /31 subnet has only 2 addresses (0 usable for traditional hosts, but usable for point-to-point links). A /32 is a single host.
• Mixing up decimal and binary in the mask — A /25 mask is 255.255.255.128, not 255.255.255.192 (which is /26). Double-check your CIDR-to-mask conversion.

Frequently asked questions