Subnet Calculator: IPv4 and IPv6 Network, Hosts and Split

How to use it

Type the network in Network (CIDR), such as 192.168.1.10/24. A mask also works: 10.0.0.0 255.255.255.0.
Read Network address, First host, Last host and Usable hosts; they are the addresses a device in this subnet can use.
To split the network, type the new length in Split into prefix: 26 gives four subnets from a /24. The table lists them.

How a subnet is calculated

An address and its prefix length give the network: the prefix says how many leading bits name the network, and the rest name hosts. The network address has all host bits at 0. The broadcast address of an IPv4 subnet has them all at 1, so the usable hosts are the addresses between the two: 2 to the power of the host bits, minus 2.

hosts = 2^(32 − prefix) − 2   (IPv4)
network = address AND mask
broadcast = network OR wildcard

A /31 point-to-point link has two usable addresses, both of them host addresses (RFC 3021, section 2.1).
A /32 is one address, used for a single host route.
IPv6 has no broadcast address, so all addresses of a range are counted.

Address ranges and what they mean

Some blocks of addresses have fixed uses. Private IPv4 addresses (RFC 1918) work only inside a network, the shared space of RFC 6598 is used by carriers, and documentation blocks (RFC 5737 for IPv4, RFC 3849 for IPv6) are reserved for examples and never routed on the internet. The page reports the range a subnet sits in; a larger subnet that covers several ranges is reported as wide.

IPv6 text is shown in the compressed form of RFC 5952: lower case, no leading zeros, and the longest run of zero groups written as two colons.

Splitting a network

A split gives the subnets of a new, longer prefix. Each step of the new prefix doubles the number of subnets: a /24 split into /25 gives two subnets, into /26 four, into /27 eight. The page lists up to 1,024 subnets and always shows the total.

Example: 192.168.1.10/24 split into /26

The address 192.168.1.10 with a /24 prefix is in the network 192.168.1.0. Its usable hosts run from 192.168.1.1 to 192.168.1.254, which is 254 addresses. The address is in private space (RFC 1918).

Splitting it into /26 gives four subnets of 62 usable hosts each: 192.168.1.0/26, 192.168.1.64/26, 192.168.1.128/26 and 192.168.1.192/26.

Measure	Value
Network	192.168.1.0
Broadcast	192.168.1.255
Usable hosts	254
Subnet mask	255.255.255.0
Wildcard mask	0.0.0.255
Subnets after a split into /26	4

Frequently asked questions

What is the difference between a network and a host address?

The network address names the subnet itself and cannot be given to a device. A host address is any address inside the subnet that a device can use. The broadcast address is the last one, and it is not a host either.

Why does a /31 have two usable addresses?

On a point-to-point link between two routers there are only two ends, so RFC 3021 lets both addresses of a /31 be used as host addresses, with no network or broadcast address.

What is a wildcard mask?

It is the subnet mask with its bits inverted. Access lists and some routing protocols use it to say which bits must match, so 0.0.0.255 means the last octet is free and the first three must match.

Can I enter a subnet mask instead of a prefix length?

Yes. Type the address, a space and the mask, such as 10.0.0.0 255.255.255.0. A mask with its ones and zeros mixed is refused, because no prefix length can describe it.

How do I split an IPv6 network?

Enter the IPv6 network with its prefix and the new prefix in the split field. A /48 split into /64 gives 65,536 subnets. The page lists the first 1,024 and shows the total.

Does this tool send my addresses anywhere?

No. The calculation runs in your browser, and nothing you type is sent or stored.

Sources

Figures and text last checked on Tuesday, November 10, 2026.

Result