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IP Subnet Calculator

Calculate network address, broadcast address, usable host range, and total hosts from any IPv4 CIDR notation.

What is IP Subnet Calculator?

The IP Subnet Calculator takes an IPv4 address and subnet mask (or CIDR prefix length) and computes all essential network information: the network address, broadcast address, first and last usable host addresses, and the total number of usable hosts.

How to use

  1. 1 Enter an IPv4 address in dotted-decimal format, e.g. 192.168.1.100.
  2. 2 Enter the subnet mask as CIDR prefix (e.g. /24) or as a dotted-decimal mask (e.g. 255.255.255.0).
  3. 3 Click Calculate to compute the subnet details.
  4. 4 Review the network address, broadcast address, and usable host range.
  5. 5 Use the host count to determine how many devices the subnet can support.

Formula

Number of usable hosts = 2^(32 − prefix_length) − 2. Network address = IP AND subnet_mask. Broadcast = IP OR (NOT subnet_mask). First host = network + 1. Last host = broadcast − 1.

Example calculation

192.168.1.100/24 → network 192.168.1.0, broadcast 192.168.1.255, first host 192.168.1.1, last host 192.168.1.254, usable hosts = 254.

Frequently asked questions

Why subtract 2 from the host count?

The network address (all host bits 0) and the broadcast address (all host bits 1) are reserved and cannot be assigned to devices.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation appends a slash and prefix length to an IP address, e.g. /24, indicating how many bits are used for the network portion.

What is a /32 subnet?

A /32 has exactly one IP address — it is used for host routes and loopback addresses. There are 0 usable hosts in the traditional sense.

Can I enter the subnet as a dotted mask?

Yes — enter values like 255.255.255.0 in the mask field. The calculator accepts both CIDR prefixes and dotted-decimal masks.

What is a private IP range?

RFC 1918 defines three private ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These are not routable on the public internet.