Subnet Count Calculator

About this calculator

In CIDR notation, a network's prefix length (like /24) determines its size; splitting a block with parent prefix p into smaller subnets with child prefix c yields 2^(c − p) subnets, and each of those subnets has 2^(32 − c) total addresses, of which 2^(32 − c) − 2 are usable for hosts (the first address is the network address, the last is the broadcast address). This calculator applies both formulas to show how many subnets a given split creates and how many hosts each one can hold.

Network engineers and system administrators use this daily when subnetting an IP range for a new office, VLAN, or department, cloud infrastructure engineers use it when carving VPCs and subnets in AWS, Azure, or GCP, and students studying for networking certifications like the CCNA use it to practice and check subnetting problems by hand.