What a subnet is
A subnet is a block of IP addresses that belong together, such as all the devices on an office network. It is written as an address and a prefix length: 192.168.1.0/24 means the first 24 bits name the network and the last 8 bits number the devices in it — 256 addresses, of which 254 can be given to devices.
What the results mean
- Network address — the first address, which names the subnet itself.
- Broadcast address — the last address, used to reach every device at once.
- Usable hosts — everything in between, for computers, phones, printers and servers.
- Subnet mask — the prefix written as an address, such as 255.255.255.0 for /24. The wildcard mask is its opposite, used in firewall and router rules.
- /31 and /32 — special cases: /31 is used for links between two routers (RFC 3021) and /32 means a single address.
How to use the subnet calculator
- Type an address with its prefix (192.168.1.10/24), or an address and mask (192.168.1.10 255.255.255.0), or choose the prefix from the list.
- Read the network details. Private, shared and documentation ranges are recognised.
- Split the network to see the smaller subnets it divides into.
Frequently asked questions
How many hosts are in a /24?
256 addresses, of which 254 are usable: the first is the network address and the last the broadcast address.
What is the difference between /24 and 255.255.255.0?
Nothing — they are two ways of writing the same mask. /24 counts the network bits; 255.255.255.0 writes them as an address.
Does it work with IPv6?
Yes. Enter an IPv6 address with a prefix, such as 2001:db8::/48, to see the network, the first and last address and how many /64 networks it holds.