Free IP Subnet Calculator
Type an IP address with a /prefix or subnet mask and get every subnet detail at once, from usable hosts to the binary view. Works offline.
IP Subnet Calculator: Type an IP address with a /prefix or subnet mask and get every subnet detail at once, from usable hosts to the binary view. Works offline. It is free, needs no sign-up and runs in your browser. How to use it: 1) enter an IP address with a prefix, such as 192.168.1.10/24, or with a mask after a space; 2) optionally pick a prefix from the list or choose a smaller size to split the network; 3) read the results, copy the details or download the subnet list as CSV. An IPv4 address is a 32 bit number. The prefix, such as /24, says how many of those bits belong to the network.
How the IP subnet calculator works
An IPv4 address is a 32 bit number. The prefix, such as /24, says how many of those bits belong to the network. The calculator builds the subnet mask from the prefix, then applies it to your address with a bitwise AND to find the network address. Setting all host bits to one gives the broadcast address.
Formulas
- Total addresses = 2 to the power of (32 minus prefix).
- Usable hosts = total minus 2, because the network and broadcast addresses cannot be assigned.
- Wildcard mask = the subnet mask with every bit flipped. Cisco ACLs and OSPF use it.
A /31 has two usable addresses for point to point links (RFC 3021) and a /32 is a single host.
Splitting networks
Choose a longer prefix to see every smaller subnet inside your network, with its first host, last host and broadcast address. The CSV export is handy for IP address plans.
IPv6
For IPv6 the tool shows the compressed and expanded address, the network prefix, the first and last address, the total number of addresses, the address type and the reverse DNS name. IPv6 has no broadcast address and a /64 is the normal size for one LAN.
Limitations
The tool does math only. It cannot tell whether an address is in use on your network, and it does not check routing or firewall rules. Subnet splitting is limited to IPv4 and the CSV export is capped at 65,536 rows.
IP Subnet Calculator FAQs
How many usable hosts are in a /24 subnet?
A /24 has 256 addresses in total. The first is the network address and the last is the broadcast address, so 254 addresses can be given to devices. With a mask of 255.255.255.0, hosts run from .1 to .254. Each step down in prefix doubles the size, so a /23 has 510 usable hosts.
What is the difference between a subnet mask and a wildcard mask?
A subnet mask marks the network bits with ones, such as 255.255.255.0. A wildcard mask is the exact opposite, 0.0.0.255, and marks the bits that may change. Routers from Cisco and other brands use wildcard masks in access lists and OSPF network statements. This calculator shows both for any prefix.
What does CIDR notation like /26 mean?
CIDR notation writes the number of network bits after a slash. A /26 means the first 26 bits are the network and 6 bits are left for hosts. That gives 64 addresses and 62 usable hosts, with a mask of 255.255.255.192. CIDR replaced the old fixed Class A, B and C networks in 1993.
Does this subnet calculator support IPv6?
Yes. Enter an IPv6 address with a prefix, such as 2001:db8::/48, to see the network prefix, the first and last address, the number of addresses and how many /64 networks fit inside. It also shows the full expanded form and the reverse DNS name. Splitting into subnets is available for IPv4 only.
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