🖧 Subnet Calculator
Enter an IPv4 address and a CIDR prefix to get the network and broadcast addresses, subnet and wildcard masks, the usable host range, and the total and usable host counts — no binary maths required.
🌐 IPv4 / CIDR, Worked Out
What is a Subnet Calculator?
Subnetting carves an IP address space into smaller, manageable networks. Given an address and a CIDR prefix, this calculator applies the subnet mask with bitwise logic to reveal the network boundaries, the assignable host range, and the address counts — the figures you need to design VLANs, size DHCP scopes, or debug a routing problem.
Use it to plan address allocation or sanity-check an existing layout. The results follow standard IPv4 rules but are estimates for planning — verify against your real network configs before you deploy.
❓ Frequently Asked Questions
What does a subnet calculator do?
It takes an IPv4 address and a CIDR prefix (like /24) and derives everything you need to plan or troubleshoot a network: the network address, the broadcast address, the subnet and wildcard masks, the first and last usable host addresses, and how many total and usable hosts the block holds. It saves you doing the binary maths by hand.
Why are there two fewer usable hosts than total addresses?
In a standard subnet the first address is reserved as the network identifier and the last as the broadcast address, so neither can be assigned to a host. That's why a /24 has 256 total addresses but only 254 usable ones. The /31 and /32 prefixes are special cases — /31 is used for point-to-point links where both addresses are usable, and /32 identifies a single host.
What is the wildcard mask used for?
The wildcard mask is the bitwise inverse of the subnet mask. It's most often used in access control lists and routing protocols like OSPF, where matching rules specify which bits to ignore. A /24 subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255.
Is this accurate enough to configure real equipment?
The maths follows standard IPv4 addressing exactly, so the addresses and counts are correct. Still, treat the output as a planning estimate and verify it against your actual switch, router, firewall, and DHCP configs before deploying — overlapping ranges and reserved addresses in your environment matter too.