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Subnet Calculator

The subnet calculator takes an IPv4 address in CIDR notation and returns the network and broadcast addresses, the subnet and wildcard masks, the usable host range and how many hosts the block holds. It accepts a dotted mask instead of a prefix length, and says whether the address is public, private or reserved.

Address and prefix 0 characters
Subnet

Your result will appear here.

Not sure where to start? Use Load example.

Results update automatically and are calculated on your device. Nothing you type is sent to a server.

Runs in your browser. Processing happens entirely in your browser. Nothing you enter is sent to Delimiter.live.

How to use the Subnet Calculator

  1. Enter an address in CIDR notation, such as 192.168.1.0/24.
  2. A dotted mask works too — 192.168.1.0/255.255.255.0 gives the same answer.
  3. Read the network and broadcast addresses and the usable host range.
  4. If you entered a host address rather than the network address, the note at the top tells you which network it belongs to.

Example

Input
192.168.1.0/24
Output
Network: 192.168.1.0
Broadcast: 192.168.1.255
Usable: 192.168.1.1 – 192.168.1.254 (254 hosts)

Common use cases

  • Working out how many hosts a proposed subnet will hold before allocating it.
  • Finding which network a given host address belongs to.
  • Converting between a prefix length and a dotted subnet mask.
  • Producing the wildcard mask for an access control list.
  • Checking whether an address is public, RFC 1918 private, or reserved.

Limitations and things to watch for

  • IPv4 only. IPv6 subnetting works on the same principles but the address sizes make a different interface sensible, so it is not folded in here.
  • A /31 has no network or broadcast address and carries two usable addresses for point-to-point links (RFC 3021); a /32 is a single host. Both are handled, but older equipment may not accept a /31.
  • This calculates from the numbers you give it. It does not query anything, so it cannot tell you whether an address is actually in use.

Frequently asked questions

Why are there two fewer usable hosts than total addresses?
The first address in a block identifies the network itself and the last is the broadcast address, so neither can be assigned to a host. A /24 therefore holds 256 addresses but 254 usable ones. The exceptions are /31 and /32.
What is a wildcard mask?
The bitwise inverse of the subnet mask — 0.0.0.255 where the mask is 255.255.255.0. Cisco access control lists and some routing protocols use it instead of the subnet mask, and getting the two confused is a common source of rules that match nothing.
Can I enter a host address instead of the network address?
Yes. Give it 10.20.30.40/22 and it works out that the network is 10.20.28.0/22, and says so in a note so the difference is not hidden from you.
What does a /31 mean?
A two-address block for a point-to-point link, defined by RFC 3021. Because there are only two addresses and no other hosts to broadcast to, both are usable rather than being spent on network and broadcast addresses.
Does this run on your server?
No. Subnetting is arithmetic on the address you type, with no lookup involved, so it runs entirely in your browser and nothing is transmitted.

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