Subnet Calculator

Frequently Asked Questions

What does the /24 or /16 mean after an IP address (CIDR notation)?

CIDR (Classless Inter-Domain Routing) notation expresses the network prefix length — the number of bits in the subnet mask set to 1. /24 means 24 bits for network, 8 bits for hosts (255.255.255.0), giving 256 addresses (254 usable hosts). /16 means 16 network bits (255.255.0.0), giving 65,536 addresses.

How many usable hosts does a subnet have?

Usable hosts = 2^(32 − prefix length) − 2. Two addresses are reserved: the network address (all host bits = 0) and the broadcast address (all host bits = 1). So a /24 has 2^8 − 2 = 254 usable hosts. A /30 (common for point-to-point links) has 2^2 − 2 = 2 usable hosts.

What are the private IP address ranges?

RFC 1918 defines three 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), and 192.168.0.0/16 (192.168.0.0 – 192.168.255.255). These are not routable on the public internet and are used for internal networks behind NAT.

What is the difference between network address, broadcast address, and host range?

The network address is the first address in the subnet (all host bits 0) — it identifies the subnet itself and cannot be assigned to a host. The broadcast address is the last address (all host bits 1) — packets sent here reach all hosts in the subnet. The host range is every address in between, which can be assigned to devices.

How do I split a network into smaller subnets (subnetting)?

To create 2 subnets from a /24, increase the prefix by 1 to /25 — this splits the range into two halves. For 4 subnets, use /26. Each additional bit doubles the number of subnets but halves the host count per subnet. This is called Variable Length Subnet Masking (VLSM).