Subnet Calculator
Compute CIDR, netmask, host range and broadcast.
Enter a target
e.g. 192.168.1.0/24 — press ⏎ / ⌘⏎
What is Subnet Calculator?
The Subnet Calculator derives netmask, wildcard mask, network address, broadcast address, usable host range and total address count from CIDR notation.
The first address in every network is the network address and the last is broadcast, neither assignable to a host — so a /24 has 256 addresses but 254 usable. A /31, per RFC 3021, uses both addresses on point-to-point links.
The wildcard mask is the netmask's inverse, used mainly in Cisco access lists and OSPF configuration to match address ranges. Everything is computed in your browser.
Frequently Asked Questions
8 questionsWhat is CIDR notation?
The "address/prefix" form like 192.168.1.0/24; /24 means the first 24 bits are the network part. Bigger prefix = smaller network: /24 = 256 addresses, /25 = 128, /26 = 64.
Why is usable hosts total minus 2?
The first address is the network address and the last is broadcast — neither can be assigned to a host. A /24 has 256 addresses but 254 usable.
Why are /31 and /32 special?
/32 identifies a single host (host route). /31, per RFC 3021, uses both addresses on point-to-point links with no broadcast — common on router-to-router links.
What is the wildcard mask for?
It's the inverse of the netmask (e.g. 0.0.0.255), used mainly in Cisco ACLs and OSPF configuration to match address ranges.
How do I split a network in two?
Increase the prefix by one: a /24 splits into two /25s (128 addresses each), a /25 into two /26s, and so on. Each step halves the address count.
Which ranges are private?
RFC 1918 defines three: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Additionally 100.64.0.0/10 is carrier NAT (CGNAT), 169.254.0.0/16 is link-local and 127.0.0.0/8 is loopback.
What is VLSM?
Variable-length subnet masking — using differently sized subnets within one network. A /27 for a 20-host office, a /30 for a router-to-router link. It cuts address waste substantially.
How is subnetting different in IPv6?
The habits change: a standard end-user network is a /64 and going narrower is discouraged (SLAAC stops working). Organisations typically receive a /48, which is 65,536 /64 subnets — the priority is orderly planning, not conserving addresses.