How it works
This calculator answers everyday networking questions without a spreadsheet: which network an IP belongs to, how many hosts fit in a block, what the broadcast is, or how to split a network into subnets.
Type an address with its prefix (10.20.30.40/16), with its netmask (10.20.30.40 255.255.0.0) or on its own. You get the network in CIDR notation, the full range, the netmask, the wildcard, the broadcast, the first and last usable host and the number of addresses. You also see the address as an integer, in hexadecimal and in binary, its reverse DNS name and its IPv4-mapped IPv6 form.
The type label tells you whether the IP is public, private (RFC 1918), CGNAT, loopback, link-local, multicast or reserved for documentation. It helps explain why an address is not reachable from the internet.
Under Subnets, pick a longer prefix and get the resulting blocks, which is handy when planning VPCs, VLANs or firewall rules. If you type a range such as 10.0.0.1 - 10.0.0.9, the tool returns the smallest list of CIDR blocks that covers it exactly.
Everything works the same with IPv6. The math uses 128-bit integers in your browser and never calls a server.
Examples
IPv4 /22 block
192.168.10.37/22
Network 192.168.8.0/22 Range 192.168.8.0 – 192.168.11.255 Netmask 255.255.252.0 (/22) Wildcard 0.0.3.255 Broadcast 192.168.11.255 Usable hosts 192.168.8.1 – 192.168.11.254 Hosts 1,022 Type Private (RFC 1918)
Range to CIDR blocks
10.0.0.1 - 10.0.0.9
10.0.0.1/32 10.0.0.2/31 10.0.0.4/30 10.0.0.8/31
Frequently asked questions
Why does a /24 have 254 hosts instead of 256?
In IPv4 the first address identifies the network and the last one is the broadcast, so neither is assigned to a device. The exceptions are /31, used on point-to-point links (RFC 3021), and /32, which is a single address.
What is the wildcard?
It is the inverted netmask: ones where the mask has zeros. Cisco ACLs and some firewall rules use it to say which bits may vary.
Can I type the netmask instead of the prefix?
Yes. It accepts 192.168.1.10/24, 192.168.1.10/255.255.255.0 and 192.168.1.10 255.255.255.0. If the mask has gaps, like 255.0.255.0, it tells you it is invalid.
Does it work with IPv6?
Yes: it shows the network, the range, the expanded and RFC 5952 short forms, reverse DNS under ip6.arpa and the address type (global, ULA, link-local, documentation and so on).