Subnet Calculator

Calculate subnets, broadcast addresses, and host ranges for IP addresses.

Example: 192.168.0.1/29

What Is a Subnet Calculator?

IzHost Subnet Calculator is a free network tool that, given an IP address and subnet mask (CIDR), instantly computes the network address, broadcast address, first/last usable host, total usable host count and IP type. Define correct ranges without mistakes when configuring servers, planning VLANs and writing firewall rules.

Subnetting splits an IP block into smaller networks, letting you use address space efficiently and isolate network traffic. This calculator does the complex binary math for you, speeding up network design and preventing connectivity issues caused by an incorrect mask.

Calculated Values

Network & Broadcast Address

Computes the network address and broadcast address for your IP/CIDR. These addresses cannot be assigned to hosts and are essential for determining the correct host range.

Usable Host Range

Shows the first and last assignable host address and the total usable host count. See exactly which IP range you can assign to servers and devices.

Subnet Mask & CIDR

Converts the CIDR prefix (e.g. /24) to a dotted-decimal subnet mask (e.g. 255.255.255.0) and vice versa. Use the correct mask format in your configurations.

IP Type Detection

Determines whether the address is public, private, loopback or multicast. Make routing and security decisions based on the correct type.

Frequently Asked Questions

What does CIDR (/24, /16) mean?
The CIDR prefix is the number of fixed (1) bits in the subnet mask. /24 means the first 24 bits are the network part (255.255.255.0) and there are 254 usable hosts. A smaller prefix (e.g. /16) means a larger network with more hosts.
How many usable hosts are in a /24 network?
A /24 network has 256 addresses; subtracting the network and broadcast addresses leaves 254 usable hosts. The calculator shows this value automatically for every CIDR.
Why can't the network and broadcast addresses be used as hosts?
The network address (first address) identifies the network itself; the broadcast address (last address) is reserved to send packets to all devices on the network at once. Therefore neither can be assigned to a device.
What are the private (RFC 1918) IP ranges?
The private ranges defined by RFC 1918 are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. These addresses are not routed on the internet and are used on local networks. The calculator detects the IP type automatically.
Can I use it for VLSM (variable-length subnet masks)?
Yes. By entering different CIDR prefixes you can size each subnet individually and pick the mask that best fits the number of hosts you need.
Does this tool support IPv6?
This calculator is optimised for IPv4 subnetting. For IPv6 planning or advanced networking needs, contact the IzHost support team.