What Is an IP Subnet Calculator?
An IP subnet calculator computes network and broadcast addresses, usable host ranges, and subnet masks from a given IP address and prefix length (CIDR notation). It is an essential tool for network engineers and system administrators who need to plan IP address allocation, design network segments, or troubleshoot routing issues.
How to Use This IP Subnet Calculator
- Enter an IPv4 address and a subnet mask or CIDR prefix length (e.g., 192.168.1.0/24).
- View the calculated network address, broadcast address, usable host range, and total number of hosts.
- Adjust the prefix length to explore different subnet sizes and plan your network topology accordingly.
Key Concepts
Subnetting divides a larger network into smaller, more manageable segments. The subnet mask determines which bits of an IP address identify the network and which identify individual hosts. A /24 prefix provides 254 usable addresses, a /25 gives 126, and so on—each additional bit halves the available hosts. CIDR (Classless Inter-Domain Routing) replaced the old Class A/B/C system and allows flexible allocation of address space.
Hosts = 2(32 − Prefix) − 2, Network = IP AND Subnet Mask
Frequently Asked Questions
What does CIDR notation mean?
CIDR notation appends a slash and a number (e.g., /24) to an IP address. The number indicates how many leading bits form the network portion. A /24 means the first 24 bits are the network address, leaving 8 bits (256 addresses, 254 usable) for hosts.
Why are two addresses reserved in every subnet?
The first address in a subnet is the network address (identifies the network itself) and the last is the broadcast address (sends packets to all hosts on the subnet). Neither can be assigned to a device, so a /24 subnet has 254 usable addresses, not 256.
What is the difference between public and private IP ranges?
Private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are reserved for internal networks and are not routable on the public internet. Public IP addresses are globally unique and assigned by regional internet registries. NAT (Network Address Translation) bridges private networks to the public internet.