IP Subnet Calculator
Calculate subnet mask, network address, broadcast address, and usable hosts for any CIDR.
What Is the IP Subnet Calculator?
The IP Subnet Calculator computes network address, broadcast address, usable host range, number of hosts, wildcard mask, and subnet information for any IPv4 address and subnet mask (or CIDR notation). Essential for network design, firewall configuration, and IP address management.
Formula
How to Use
Enter an IPv4 address (e.g., 192.168.1.100) and either a subnet mask (e.g., 255.255.255.0) or CIDR prefix length (e.g., /24). The calculator shows the network address, broadcast address, first and last usable host addresses, total number of hosts, and the binary representations of the address and mask.
Example Calculation
IP: 192.168.1.100, Subnet: /24 (255.255.255.0): Network = 192.168.1.0. Broadcast = 192.168.1.255. Usable hosts: 192.168.1.1 to 192.168.1.254 (254 hosts). /25 splits this into two /25 subnets of 126 hosts each.
Understanding IP Subnet
IP subnetting is the practice of dividing an IP network into smaller subnetworks. Each subnet has a network address (identifies the subnet), a broadcast address (addresses all hosts on the subnet), and a range of assignable host addresses between them. The subnet mask defines which bits of the IP address represent the network vs host portions.
Classless Inter-Domain Routing (CIDR) replaced the inflexible Class A/B/C system in 1993, allowing networks of any size to be defined with prefix notation. A /24 network has 254 usable hosts; a /16 has 65,534. Subnetting allows one large network block (e.g., 192.168.1.0/24) to be divided into smaller subnets (two /25s, four /26s, etc.) for organizational purposes.
Subnet calculation is a daily task for network engineers and system administrators designing LANs, configuring firewalls and access control lists, setting up VLANs, troubleshooting routing issues, and managing IP address allocation (IPAM). Misconfigurations in subnet masks are a common source of network connectivity problems — using this calculator helps verify configurations before deployment.
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation expresses a network as IP/prefix, where prefix is the number of 1-bits in the subnet mask. /24 = 255.255.255.0 (24 ones), /8 = 255.0.0.0. CIDR replaced classful networking (Class A/B/C) in 1993.
Why is the number of usable hosts 2^n − 2?
The first address in a subnet is the network address (not assignable), and the last is the broadcast address. So from 2^n total addresses, 2 are reserved, leaving 2^n − 2 usable host addresses.
What are private IP address ranges?
RFC 1918 private ranges: 10.0.0.0/8 (10.0.0.0–10.255.255.255), 172.16.0.0/12 (172.16.0.0–172.31.255.255), 192.168.0.0/16 (192.168.0.0–192.168.255.255). These are not routable on the internet.
What is subnetting used for?
Subnetting divides a large network into smaller segments, improving security (isolating network segments), performance (reducing broadcast domains), and address efficiency (allocating only needed IP ranges to each segment).
Is this calculator free?
Yes, completely free with no account required.
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