Subnet Calculator

The subnet calculator turns the question of how many hosts fit in a block into one input with every answer shown, a common tool for network operations, data center planning and firewall rules:

• Two notations: prefix form 192.168.1.100/26 and dotted mask form 192.168.1.100 255.255.255.192 both work
• Full subnet parameters: network address, subnet mask, wildcard mask, broadcast address and usable host range
• Host counts: total addresses and usable hosts after removing the network and broadcast addresses, with standard handling for /31 and /32
• Binary view: IP and mask expanded per octet so network and host bits are visible
• Range classification: identifies private, loopback, link-local, carrier-grade NAT, multicast, reserved or public addresses
• Quick prefix switch: jump between /8 and /31 while comparing capacity

When to use it

• Planning VLANs and checking how many endpoints each segment can hold
• Confirming segment boundaries and wildcard masks for switches, firewalls and ACLs
• Filling cloud security group ranges without a CIDR typo that opens too much
• Diagnosing why two hosts cannot ping each other by checking they share a subnet
• Checking answers for subnetting exercises in a networking course

Common questions

• Why only 254 hosts on a /24? A /24 holds 2 to the 8th, or 256 addresses; the network and broadcast addresses take one each, leaving 254 for hosts
• What is a wildcard mask? It is the bitwise inverse of the mask, so a /26 mask 255.255.255.192 gives 0.0.0.63, the form used by Cisco ACLs and OSPF network statements
• What about /31 and /32? A /32 is a single host address; a /31 follows RFC 3021 for point-to-point links where both addresses are usable, so two hosts
• How do I know two IPs share a subnet? AND each IP with the mask; equal results mean the same subnet, and the binary view here makes that comparison direct

Common prefix reference

To check where a public IP is registered, use the IP lookup tool; to split a URL into host, port and parameters, use the URL parser. All calculations run in the browser and the IP you enter is never uploaded.