Subnet / VLSM Calculator

Split a network into subnets, or check what a CIDR actually covers.

Why this exists

IP space is handed out in CIDR blocks, and every firewall rule, VPC and VLAN plan starts with knowing exactly which addresses a block covers. Used daily when carving a network into per-team or per-service subnets.

🔒 Runs in your browser — nothing is sent anywhere

Network (CIDR)An address with a prefix, e.g. 10.0.0.0/8

Split into subnets of prefixMust be equal to or longer than the network's own prefix.Or: aggregate a list into minimal CIDRsThe reverse of splitting — paste IPs or blocks (one per line or comma-separated) and get the smallest exact covering set, for shorter firewall rules and allow-lists.

Network: 192.168.1.0
Broadcast: 192.168.1.255
First host: 192.168.1.1
Last host: 192.168.1.254
Netmask: 255.255.255.0
Wildcard: 0.0.0.255
Total addresses: 256
Usable hosts: 254

Subnet	Range	Hosts
192.168.1.0/26	192.168.1.1 – 192.168.1.62	62
192.168.1.64/26	192.168.1.65 – 192.168.1.126	62
192.168.1.128/26	192.168.1.129 – 192.168.1.190	62
192.168.1.192/26	192.168.1.193 – 192.168.1.254	62

🧮Subnet / VLSM Calculator

Subnet / VLSM Calculator