IP Subnet Calculator
Enter any IPv4 address and a CIDR prefix to get the complete subnet summary: network and broadcast addresses, subnet and wildcard masks, the usable host range, and host counts. Everything is computed in your browser as you type.
Subnet details
Example: 192.168.1.128/26 has 62 usable hosts.
How subnetting works
An IPv4 address is 32 bits. A subnet splits those bits in two: the leading bits (set by the
prefix length) identify the network, and the remaining bits number the hosts inside it. The
subnet mask writes the same split as dotted decimal — a /26 is
255.255.255.192, because its first 26 bits are ones.
Worked example, as computed by this calculator's engine: 192.168.1.130/26. Six host bits give blocks of 64 addresses, so the address falls in the block starting at 192.168.1.128 with broadcast 192.168.1.191, usable hosts 192.168.1.129 through 192.168.1.190 — 62 usable of 64 total.
Network, broadcast, and the two lost addresses
Within each block, the all-zeros host value names the subnet itself and the all-ones value is the broadcast address, which is why usable hosts = total − 2 for ordinary prefixes. Point-to-point /31 links (RFC 3021) and /32 host routes are the deliberate exceptions, and the calculator reports them explicitly rather than showing a negative host count.
Private address ranges
Three ranges are reserved for private networks: 10.0.0.0/8,
172.16.0.0/12, and 192.168.0.0/16. Home and office networks almost
always use them, which is why router addresses like 192.168.1.1 look so familiar. The
calculator labels every result as private or public so you can spot a misconfigured range at a
glance.
Frequently asked questions
What does CIDR notation like /24 mean?
The number after the slash is how many leading bits of the address identify the network; the remaining bits identify hosts. A /24 leaves 8 host bits → 256 addresses; a /26 leaves 6 → 64 addresses. Bigger prefix number = smaller network.
Why are two addresses missing from the usable count?
In every ordinary subnet the all-zeros host address names the network itself and the all-ones address is the broadcast address, so a /24 has 256 addresses but 254 usable hosts. The exceptions are /31 point-to-point links (both addresses usable, RFC 3021) and /32 single-host routes.
What is a wildcard mask?
The bitwise inverse of the subnet mask — 255.255.255.192 inverts to 0.0.0.63. Router access-control lists (notably Cisco ACLs) use wildcard masks to say which address bits are allowed to vary.
Which addresses are private?
RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private networks. They are not routable on the public internet; traffic from them reaches the internet through NAT. The calculator flags whether your input falls in these ranges.
Addresses are processed locally in your browser and never transmitted. Formulas are implemented as tested, typed functions — see the methodology page. Verify allocations against your network documentation before making production changes.