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CIDR / Subnet Calculator

Network, broadcast, host range, and masks from any IPv4 CIDR block.

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IP address / prefix (CIDR notation)
Network address192.168.1.0
Broadcast address192.168.1.255
First usable host192.168.1.1
Last usable host192.168.1.254
Usable hosts254
Total addresses256
Subnet mask255.255.255.0
Wildcard mask0.0.0.255
CIDR192.168.1.0/24
mask    11111111.11111111.11111111.00000000
network 11000000.10101000.00000001.00000000
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01 · Real-world fits

Common use cases

  • Sizing a VPC or VLAN — checking how many hosts a /22 actually gives you
  • Writing firewall or ACL rules that need the wildcard mask
  • Splitting an office network into per-floor subnets without overlap
  • Decoding a CIDR block in a cloud console or a colleague's network diagram
  • Teaching or learning subnetting with the binary view as the ground truth
02 · The honest pitch

Why CIDR / Subnet Calculator?

Subnetting is pure bit arithmetic, and doing it in your head under pressure is how overlapping ranges ship to production. This calculator shows the answer and the binary working — where the prefix boundary falls, why a /24 has 254 usable hosts rather than 256, and it handles the modern edge cases (RFC 3021 /31 point-to-point links) that older calculators get wrong. It runs offline once loaded, which is occasionally exactly what you need when the network you are debugging is the one you are on.

03 · Edge cases

Frequently asked questions

Every conventional subnet reserves its first address as the network identifier and its last as the broadcast address. A /24 spans 256 addresses, so 254 remain assignable to hosts. The exceptions: /31 blocks (both addresses usable, per RFC 3021, for point-to-point links) and /32 (a single host route).