What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length to define a network block. The prefix length (e.g., /24) indicates how many bits are used for the network portion. For example, 192.168.1.0/24 means the first 24 bits are the network, leaving 8 bits for host addresses — supporting 254 usable hosts.

What is the difference between a subnet mask and a wildcard mask?

A subnet mask uses 1s in the network portion and 0s in the host portion (e.g., 255.255.255.0 for /24). A wildcard mask is the inverse — 0s where the subnet mask has 1s and 1s where it has 0s (e.g., 0.0.0.255 for /24). Wildcard masks are commonly used in Cisco ACLs and OSPF routing configurations.

How do I calculate the number of usable hosts?

For a /n prefix, total hosts = 2^(32-n). Usable hosts = total hosts - 2, because the first address is the network address and the last is the broadcast address. Exception: /31 networks (used for point-to-point links) and /32 (single host) have all addresses usable under RFC 3021.

What are private IP address ranges?

Private IP ranges defined by RFC 1918 are: 10.0.0.0/8 (10.x.x.x), 172.16.0.0/12 (172.16.x.x to 172.31.x.x), and 192.168.0.0/16 (192.168.x.x). These are not routable on the public internet and are used for local networks, corporate intranets, and home routers.

What is a broadcast address?

The broadcast address is the last address in a subnet range. Packets sent to this address are delivered to all hosts in the subnet. It is formed by setting all host bits to 1 in the network address. For example, in 192.168.1.0/24, the broadcast address is 192.168.1.255.

Subnet Calculator

Calculate subnet information from an IP address and CIDR notation. Get network address, broadcast, host range, subnet mask, and more.

IP Address / CIDR

Enter an IP address with CIDR prefix, e.g. 192.168.1.0/24

Network Address	192.168.1.0
Subnet Mask	255.255.255.0
Broadcast Address	192.168.1.255
First Usable Host	192.168.1.1
Last Usable Host	192.168.1.254
Wildcard Mask	0.0.0.255
Total Hosts	256
Usable Hosts	254
IP Class	C
Address Type	Private

Binary Representation

IP Address: 11000000.10101000.00000001.00000000

Subnet Mask: 11111111.11111111.11111111.00000000

Network: 11000000.10101000.00000001.00000000

How to Use

Calculate subnet information from an IP address and CIDR notation. Get network address, broadcast, host range, subnet mask, and more.

1Type an IP address with its CIDR prefix into the input field — for example, 192.168.1.0/24. Or click one of the example buttons below the field to auto-fill a common network.
2The calculator instantly shows the network address, subnet mask, broadcast address, first and last usable hosts, total and usable host counts, IP class, and whether it is a private or public range.
3Check the Binary Representation section at the bottom to see the IP address, subnet mask, and network address in dotted binary notation — useful for visualizing how the subnet mask splits the address.
4Use the wildcard mask output directly in Cisco ACLs or OSPF configurations.
5Try the quick-fill examples (10.0.0.0/8, 172.16.0.0/12, etc.) to compare class A, B, and C subnets side by side.

Key Features

Instant CIDR calculation — network address, mask, broadcast, and host range appear as you type
Binary representation — see the IP and mask in dotted binary to understand bit-level subnet logic
Wildcard mask output — ready to paste into Cisco ACLs and routing configurations
Private/public detection — identifies RFC 1918 private address ranges automatically
Example quick-fill — common subnets (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/24) to explore immediately

Frequently Asked Questions

Learn More

Subnet Calculator Guide — CIDR, Subnet Masks & IP Ranges Explained