The Subnet Calculator takes a CIDR block and computes the network and broadcast addresses, the usable host range, the subnet mask, the total host count and the number of available subnets — the math behind IPv4 addressing plans.
Enter a CIDR block (10.20.0.0/22) and run the tool. The calculator parses the address and prefix length and returns the full subnet breakdown.
Input: CIDR block — e.g. 10.20.0.0/22.
The output shows the network address, broadcast address, first and last usable host, subnet mask, wildcard mask, total addresses and usable host count. Use these values when configuring interfaces, DHCP scopes and firewall ACLs.
→ Plan a VLAN or office network addressing scheme.
→ Calculate DHCP scope boundaries and host counts.
→ Derive wildcard masks for firewall and router ACLs.
→ Split a large block into smaller subnets for departments.
A /24 has 256 total addresses; subtracting the network and broadcast addresses leaves 254 usable hosts. A /26 has 62 usable, a /28 has 14, and a /30 has 2 (commonly used for point-to-point links).
A wildcard mask is the bitwise inverse of the subnet mask (e.g. 0.0.0.255 for a /24). It is used in Cisco ACLs and OSPF network statements to match ranges, unlike the subnet mask used in interface configuration.
Each bit you borrow doubles the number of subnets and halves their size. A /24 splits into two /25s, four /26s, eight /27s and so on. Use this calculator on each resulting block to get its exact range and host count.