IPv4 / IPv6 Subnet Calculator
Type a CIDR such as 10.0.0.0/22 or 2401:db00::/48 and get the network address, broadcast, usable host range, netmask, wildcard mask, binary form, address class, private/public flag and reverse DNS zone instantly. Results are computed in your browser; nothing is sent to a server.
Split into subnets
Splits the CIDR above. Capped at 1024 subnets.
Supernet / summarise
About CIDR notation
Classless Inter-Domain Routing (CIDR) writes an address and the number of leading network bits, for example 192.168.10.0/24. The remaining bits identify hosts: a /24 leaves 8 host bits (256 addresses), a /22 leaves 10 (1024 addresses). In IPv4 two addresses per subnet are reserved for the network and broadcast addresses, so a /24 has 254 usable hosts, except for /31 point-to-point links and /32 single hosts. IPv6 has no broadcast; the all-zeros interface identifier is the subnet-router anycast address.
The same calculation is available as JSON: POST /tools/api/v1/subnet/calc {"cidr": "10.0.0.0/22"}, POST /tools/api/v1/subnet/split {"cidr", "new_prefix"} and POST /tools/api/v1/subnet/summarise {"cidrs": [...]}. Planning private networking for a BookMyHost VPS? A /24 per project is a sensible default.
Frequently asked questions
How many usable hosts are in a /24?
254. A /24 has 256 addresses; the first is the network address and the last is the broadcast address. A /31 (point-to-point, RFC 3021) and /32 have no such reservation.
How is IPv6 different?
There is no broadcast address in IPv6. The calculator reserves only the subnet-router anycast address (the all-zeros host) in prefixes shorter than /127.
What is a wildcard mask?
The bitwise inverse of the subnet mask, used in Cisco ACLs and OSPF network statements. For 255.255.252.0 the wildcard is 0.0.3.255.
Can I split a network into subnets?
Yes. Enter a CIDR and a new (longer) prefix to list every subnet, up to 1024 at a time, or paste several CIDRs to summarise them into the smallest supernet.
Does this send my IP ranges to a server?
Not unless you want to. The calculator runs entirely in your browser; the JSON API (POST /tools/api/v1/subnet/calc) is optional for scripts and automation.
Embed / link to this tool
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<a href="https://bookmyhost.com/tools/subnet-calculator" title="IPv4 / IPv6 Subnet Calculator by BookMyHost">IPv4 / IPv6 Subnet Calculator</a> - free tool by <a href="https://bookmyhost.com">BookMyHost</a>